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Behr, H. C., The Consolidated Gold Fields of South

Africa, Limited, P.O. Box 1167, Johannesburg,

Transvaal, South Africa. Bensusan, S. L., M.Inst.M.M., Equitable-building,

Sydney, Australia. Bhatt, Parvatiprasad Vishvanath, 55, Blenheim

crescent, Notting. hill, W. Body, John Benjamin, M.Inst.C.E., Puente de

Alvarado 15, Mexico City. Bose, S., Deputy Superintendent, Central Jail,

Jubbulpore, India. Bostwick, H. R., Messrs. Collbran and Bostwick,

Seoul, Korea. Bott, John, 37, Herne-hill, S.E. Bower, Edw. H. M., Port Office, Calingapatam,

Ganjam District, India. Brebner, Captain Charles William, Villa des Roses,

Rose-bill, Mauritius. Brelich, Henry, A.R.S.M., care of Messrs. Arnhold,

Karberg and Co., Hankow, China, Browne, Hon. John E. D., The Neale House, The

Neale, co. Mayo, Ireland. Brownell, Clarence Ludlow, 21, Hermitage-road,

Richmond, Surrey. Budge, Edward Barnard, B.Sc., M.Am. Soc.C.E.,

Engineer in Chief, ist Section, Chili State Railways (F. C. del E.), Estacion Bella Vista, Val

paraiso, Chili, South America. Bullen, William Henry Chambers, 15, St. John's.

road, Richmond, Surrey. Burt, George Stephen, F.S.S., 4, Lothbury,

E.C. Butcher, Charles Ernest, 273, Finchley-road, South

Hampstead, N.W. Buxton, John Henry, Senr., Clumber - cottage,

Montague.road, Felixstowe, Suffolk. Campbell, David B., 112, Clifton-park Avenue,

Belfast. Carolis, W. D., 18, Kayman's-gate, Colombo,

Ceylon. Chapman, Walter William, F.S.S., 5, Claremont.

road, Tunbridge Wells. Chetty, Rao Saheb T. Namberumal, B.A., 144-5,

China Bazaar-street, Sowcarpett, Madras, India. Close, Henry Gaskell, 101, Eaton-square, S.W. Dana, Prof. Charles Edmund, 2013, De Lancey-place,

Philadelphia, U.S.A. Danvers, Ernesto, F.S.S., M.Inst.E.E., 475, Piedad,

Buenos Aires, South America. Das, Hari Das, Raghunathganj, Murshedabad, India. Davy, Joseph Burtt, Cosmos Club, Washington,

D.C., U.S.A., and College of Commerce, University of California, U.S.A. Daw, Frederick R. Williams, The New Zealand

Crown Mines Company, Limited, Karangahake,

near Auckland, New Zealand. Deerhurst, Viscount, Dynes Hall, Halstead, Essex. De Marillac, Count Ernst, Wynberg, Cape Colony,

South Africa. Desborough, Captain Arthur P. H., R.A., Home

Office, Whitehall, S.W.

Donnelly, Francis, M.S.Chem. Industry, 335, Hyde.

road, Ardwick, Manchester. Donovan, Fergus, Royal Colonial Institute, North

umberland-avenue, W.C. Douslin, H. B., Public Works Department, Mata

beleland District, Rhodesia, South Africa. Dunham, Henry V., Casein Company of America,

37, Scheepmakershaven, Rotterdam, Holland. Edwards, Arthur M., Barncote, Reigate, Surrey. Ellis, Frederic Richard, F.C.S., 15, Shadwell-road,

Bishopston, Bristol. Etherington, John Francis, Hersham, Surrey. Fowler, George William, Mossel Bay, Cape Colony,

South Africa. Gallagher, J. Walter, Bangkok, Siam. Gheury, Maurice Edmund Joseph, F.P.S., 12,

Cressy-road, Hampstead, N.W. Gilfillan, W. H., Surveyor-General's Department,

Pretoria, Transvaal, South Africa. Gilkison, T. T., Mombasa, East Coast of Africa. Girouard, Lieut.-Colonel Sir Edouard Percy,

K.C.M.G., D.S.O., Johannesburg, Transvaal,

South Africa. Gleed, Richard C., Flodden-house, 21, Flodden

road, S.E. Goldblatt, D., Cape Town, South Africa. Goold, William Tom, M.I.Mech.E., Tuthill-house,

Lydney, Gloucestershire. Gray, Robert Whytlaw, 7, Orme-court, W. Halcrow, James Benjamin, 56, West-side, Wands.

worth-common, S.W., and 5, Moorgate.street.

buildings, E.C. Hamilton, John James, 1, Barkston-gardens, S.W. Hardy, James Henry, The Municipal Technical

School, Halifax. Harper, Edgar Josiah, County-hall, Spring-gardens,

S.W. Harris, Morrie J., Municipal Surveyor, Mafeking,

Cape Colony, South Africa. Hawkesle;, Charles, M. Inst.C.E., 30, Great George

street, S.W. Hawkins, Edward, Manor Estate, Sidcup, Kent. Henriques, Cecil Quixam, M.I.Mech.E., 59, Sussex.

gardens, Hyde-park, W., and 15, Victoria-street,

Westminster, S.W.. Heyer, A. E., Rosebank, Cape Town, South Africa. Hill, Walter Wellesley, Admiralty Harbour of

Refuge Works, Peterhead, N.B. Hilton, Emest Frederick, 23, The Boltons, South

Kensington, S.W., and Constitutional Club, W.C. Hipwell-Howitt, Arthur George, 2, Studdridge.

street, Hurlingham, S.W. Hke, Saw, Hsipaw Sawbwa Gyi, Hsipaw, Northern

Shan States, Burma. Hoffmann, John J., M.Inst.M.M., Rand Club.

Johannesburg, Transvaal, South Africa. Horne, James Edward, M.A., 8, Earlsfield-road,

Wandsworth.common, S.W. How, Thomas William, 1, Delahay-street, S.W. Ive, Arthur Fenwick, 85, Montague.street, Worthing,

Sussex,

Jennings, Sydney J., Messrs. H. Eckstein and Co., | Paddock, George Harrie, Mill Bank, Wellington.

P.O. Box 149, Johannesburg, Transvaal, South Salop.
Africa.

Pape, Eric, Farragut-building, Massachusetts-avenue, Kelynack, T. N., M.D., M.R.C.P., 53, Harley Boston, Massachussetts, U.S.A. street, W.

Parker, Sir Gilbert, D.C.L., M.P., 20, Carlton Kevorkian, Hagop, 3 Victoria-avenue, Bishopsgate. House-terrace, S.W. street, E.C.

Parkes, George W., The Frictionless Engine Packing Kilmer, Frederick B., Messrs. Johnson and Johnson, Company Limited, Hendham Vale Works, New Brunswick, New Jersey, U.S.A.

Harpurhey, Manchester. Kimber, Harry Watkins, Messrs. Dick, Kerr and Parnacott, Alfred Edmund, 12, Queen AdelaideCo., Limited, 110, Cannon-street, E.C.

road, Penge, S.E. Knowles, Hugh Charles, Glebe house, Sherborne. Pearse, Cecil, Ipoh, Perak, Federated Malay lane, E.C.

States. Latif, Khan Bahadur Abdul, Bopatla, Kishna District, Pearson, Charles Fellows, Redington-lodge, Reding. India.

ton-road, Hampstead, N.W. Leeds, Edward Lambert, The Brown Hoisting Peel, Hon. William Robert Wellesley, M.P., 52, Machinery Co., 39, Victoria.street, S.W.

Grosvenor-street, w.. Legg, Hugh G., P.O. Box 358, Cape Town, South Peregrino, F. Z. S., The South African Spectator, Africa.

Cape Town, South Africa. Le Roux, S. D., P.O. Box 100, Salisbuay, Rhodesia, Pincus, Fritz, P. O. Box 3, Lourenço Marques, South Africa.

Portuguese South East Africa. Letcher, John Teague, Truro, Cornwall.

Pordage, Frederick, Entebbe, Uganda, viâ Mombasa, Letcher, Thomas Henry, St. Day, Scorrier, Cornwall. East Africa. Lithgow, William T., Kingston Shipbuilding Yard Quin, Stewart Blacker, 1, Lombard-street, Belfast, Port Glasgow.

Rana, Brigadier-Col. Kumar Nur Singh, Bahadur, Littlewood, E. T., M.A., B.Sc., Wynberg High Assoc. Inst.C.E., Superintending Engineer,

School for Boys, Wynberg, Cape Colony, South | Khatmandu. Nepal, India.
Africa.

Rao, P. V. Ranganatha, B.A., B.L., Pudukotah, Lonsdale, Earl of, Lowther Castle, Penrith.

Native State, South India. Luke, James, 6, Pollock-street, Calcutta.

Reeve, Wybert, F.R.C.S., I, Bishops - mansions, Lynch, Harry Finnis Bloss, 33, Pont-street, S.W. Fulham Palace-road, S.W. Macbean, Edward, Rannochlea, St. Andrew's-drive, | Rogers, George Henry, B.Sc., Regent - house, Pollokshields, Glasgow.

Canterbury-street, New Brompton, Kent. McConnell, John, Lanzi, Campiglia Marittima, Sadgrove, Edwin J., 22, Surrey-street, Strand, W.C. Toscana, Italy.

Sano, Tojiro, Assoc.M.Inst.C.E., The City WaterMace, Prof. William Harrison, A.M., Ph.D., 127, works, Kobe, Japan.

College-place, Syracuse, New York. U.S.A. Savage, Edward Alex., A.Inst.E.E., 56, DraytonMcGregor, John, Maitland, near Cape Town, South gardens, South Kensington, S.W. Africa.

Seward, Frederick John, East London, South Africa. Marsden, Alfred, A.M.I. Mech.E., Oakley Works, Sheridan, René, Bangkok, Siam. Windsor.

Shipway, Lieut.-Colonel R. W., V.D., Grove-house, Mokhber-ed-Dowleh, His Excellency (Hossien Goli Chiswick, W. Khan), K.C.I.E., Teheran, Persia.

Shockley, William Hillman, care of Hongkong and Morris, Philip A., Rose Bank, Harrow.view, Harrow, Shanghai Banking Co., Limited, 31, LombardMurphy, Sir James, Altadore, Blackrock, Dublin

street, E.C. Murray, James P., The Toronto Carpet Manufactur. Smith, Charles Horace, 25, Howard.street, Bradford. ing Co., Limited, Toronto, Canada.

Smythe, Francis, A.JI.Inst.C.E., The Municipal Murray-Morgan, Everard Home, A.I. Mech.E., Briar Offices, Finchley, N. Lea, Prestatyn. N. Wales.

Stead, Alfred, F.R.C.I., Clement's inn, W.C. Naylor, John Alfred, A.M.I. Mech.E., 15, Cromsord Steuart, T. B., Castlegilmour, Sanquhar, N.B. road, West-bill, S.W.

Sutton, J. R., M.A., Kenilworth, Kimberley, Neville, Harry, J.P., Indwe, Cape Colony, South South Africa. Africa.

Tays, Eugene Augustus Hoffman, M.Am.S.C.E., Northcroft, G. A., Director of Public Works, Fuerte, Sinaloa, Mexico. Government Offices, Bloemfontein, Orange River Thomas, Arthur, M.Inst. M.M., Zalamea la Real, Colony, South Africa.

Huelva, Spain. Offen, Charles Rose Witcher, F.S.S., Home for Thomson, A. S., Lodna, Jherria P.O., Bengal, India. Boys, Cumberland-road, Bristol.

Tompson, Captain George Monis, M.Am.S.C.E., Owtram, B., Chinese Eastern Railway Company, Parker-road, Wakefield, Massachusetts, U.S.A.

Mining Department, Yen-tai District, New chwang, | Turnbull, Alexander, M.D., 7, Lansdowne.crescent, China.

Notting hill, W.

Wig, N. D., Messrs. Shivdev Singh Uberoi and Co., trolling results by the time he allows it to act, Punjab Iron Works, Sialkot City, India.

| he has been in the habit of keeping to his own Wilkinson, William Thompson, 49, Casella-road, time of development (varying, perhaps, only New Cross Gate, S.E.

for temperature), and altering the composition Wilson, James H. Charnock, F.R.C.I., King's

of the developer to get greater or less contrast, Leigh, Wembley, N.W.

or, to put it in another way, to get greater Wood, Frank, Messrs. Foucar and Co., Limited,

detail in one case, or greater density in Rangoon, Burma. Woodward, Harry Page, J.P., F.G.S., M.Inst.C.E.,

another case. The photographer also has got Moira Colliery, Collis Coal-field, Western Aus

into the habit of considering that he possesses tralia, and 129, Beaufort-street, Chelsea, S.W.

the power (by altering the composition of deveWright, Richard Ernest. Assoc. M.Inst.C.E., Depart. | loper) of doing more work either on the upper ment of Public Works, Port Elizabeth, South tones (adding density), or, in another case, on Africa.

the lower tones (bringing up detail), whereas, Yeoman, John Pattison, The Close, Brompton, near in nine cases out of ten, he has merely attained Northallerton, Yorkshire.

a result identical with what he would have got with an unaltered developer acting for a certain time. This older point of view is partly a

legacy from wet collodion development, where The paper read was

the presence of free silver nitrate in the deve

loper actually built up the high light deposits SOME ASPECTS OF PHOTOGRAPHIC in the negative, and partly arises from the use DEVELOPMENT.

of an imperfect alkali (ammonia) in early dryBY ALFRED WATKINS.

plate development. For the volatile nature of

ammonia often made it necessary to add more Development is the process of reducing of the alkali during the progress of developthose particles of silver salt which have been ment, and its tendency to fogging often made affected by light, to the black or metallic con- the addition of a restraining bromide necessary. dition.

These two procedures (adding more alkali to A finished negative consists of a contrast - stimulate development, and adding bromide to or series of contrasts-between tones or den restrain fog), both due to an imperfect alkali, sities. If the contrast obtained by reducing have been continued when the use of a fixed all the light-affected particles were always alkali makes either of them unnecessary, and correct, the process of development would be mysterious advantages have been attributed to simple and purely inechanical ; for after de them. In short, the development procedure of vising a developer which did not attack the a few years ago resembled the medical knowunaffected particles of silver salt, it would ledge of the 18th century, being built up of only be necessary to leave the exposed plate fads and formulæ, with no guiding principles to a sufficient time in the developer for it to do | direct it. all its work, any longer time having no further! It was the memorable paper of Messrs. action.

Hurter and Driffield (Journal Soc. Chem. But practical photographers have long found Industry, May, 1890) which pulled the comout that with most plates and subjects a placent practical photographer up with a jerk, maximum amount of development, as above and showed that his ideas on development described, is injurious, and does not give the would have to be re-constructed. The writers desired result, as the contrast between the impressed on a strip of plate a series of expotones is greater than represents the original | sures increasing in geometrical ratio, thus:--object. A certain amount of judgment has | 1, 2, 4, 8, 16, &c., and investigated the effect therefore been necessary in deciding how far of alterations in the developer. They found this reducing-or developing-action should i that the results of alterations consisted chiefly be allowed to proceed. I must point out that 'in variations of steepness of gradation or this judgment or control has been-in the past contrast between the tones) attained, but --exercised in quite a different way from what I that this was mainly a question of time, for all have indicated, and, as I shall try to point the developers (given sufficient bulk and out, in a way the coinplications of which were 'activity) were capable of attaining the quite unnecessary.

| maximum steepness or amount of contrast Instead of the photographer keeping the if sufficient time to act were allowed. They composition of his developer fixed, and con- named the degree of steepness or contrast the development factor, but it was a weak point velopment, those undotted being unaffected. that the development factor was merely a I need scarcely explain that in a graphic record of a result attained, and not a help diagram like this, no attempt is made at towards the attainment of the same result completeness ; for instance, in the part 1 all another time.

the particles are shown light-affected, whereas . In the later paper by the same authors, with long exposures in a thick film only about published in the Photographic Journal, 60 per cent. of the particles would be lightJanuary, 1898, and following months, a most affected. important light was thrown upon the action of In Fig. 2 an attempt is made to represent a bromide as a restrainer, and the great graphically what occurs when an efficient dedifferences between the results obtained by veloper has one quarter accomplished its work, different experiments (especially as regards the speed of a plate) were 'traced to the

Fig. 2. peculiar action of a bromide in the developer.

I shall not attempt, in this paper, to follow up the many proofs furnished by Messrs. Hurter and Driffield, but shall outline my own interpretation of the simple principles of development, using some illustrations borrowed

there being a comparatively feeble darkening from my recently-published manual on the

in all three tones with little contrast between subject, and shall pass on to some points

them. Fig. 3 indicates the stage when dearising from my own trials and investigations.

velopment is half over; and Fig. 4 when

development is completed, and all light-affected SIMPLE PROGRESS OF DEVELOPMENT.

FIG. 3. I throw on the screen a strip of plate which has received an increasing series of exposures in steps, from sec. to 512 secs. Incidentally this also shows the limits of the plate, for it will be seen that 64 is the maximum effective exposure, anything more than this having no increased action on the plate, while it is the minimum effective exposure, anything less than this having no action at all on the plate. The whole problem of exposure-which I am not expounding in this paper--is to bring all the light impressions which form the picture between these two limits. The upper strip is

particles completely reduced to the black developed double the time, and the contrast

metallic state. With a well balanced between the tones is increased, for while the

developer there is no effect on those particles lowest tone has increased very little in opacity,

not affected by light, but an ill-balanced the upper tones are greatly increased. Neither

developer with excessive alkali will sometimes the maximum nor the minimum limits are

attack them, this being called fog. In these altered by the longer development.

diagrams representing the simple course of Fig. 1 is an imaginary section through an

development, it will be seen that the same exposed film. Three exposures have been

proportion of work is done on each of the made on the plate, the part A being unexposed.

tones at each of the stages. But, as Messrs.

Hurter and Driffield have pointed out, an Fig. 1.

arithmetical increase in the blackened silver results in a much greater (geometric) increase in its opacity or power of stopping light, and, therefore, in the natural course of develop

ment the contrast between the tones increases B C... D....

with the length of development. This rule

applies with all developers, its limit being The circles are supposed to represent the when fog commences and when all available sensitive particles of silver salt, those dotted | light-affected silver is darkened in the darker being affected by light, and capable of dc- tones.

FIG. 4.

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Fig. 5 is an imaginary diagram of the silver to a long series of experiments, in which I representing the four tones compressed into established the fact that the time of appearsteps, and at three stages of development. ance made the correct allowance for alterations

in the activity in the developer, due to the Fig. 5.

following causes :-Temperature (between 45° and 75%); alkali in developer ; dilution of developer--pyro and amidol being an exception to this.

The time of appearance is the time elapsing between pouring on the developer and the first appearance of any trace of the image. The

multiple used to attain the required result I A B C D

have termed the multiplying factor. The multi

plying factor varies with different developing The diagonal lines indicate what is con agents, such as hydroquinone, pyro, metol, &c. veniently termed the “ steepness of gradation,” The multiplying factor is usually the same and a register of this steepness is what Messrs.

for different commercial plates, but I have Hurter and Driffield term the development

fonnd lately some plates which require a higher factor.

factor to secure sufficient contrast. These I make no attempt to discuss the question

plates are some which makers seem to turn out whether the reduction of the image is entirely in their effürts to secure a high speed reading. a chemical or partly. a physical process, and, and I notice that they are a deeper yellow than in fact, I disclaim any qualification to throw usual. It seems, therefore, that an increased light upon the chemical aspects of develop

proportion of an iodide in the emulsion alters ment.

the multiplying factor. I have found, by the

way, that a little iodide of potassium in the CONTROL OF DEVELOPMENT BY TIME.

developer very much alters the law of appearAlthough Messrs. Hurter and Driffield ex ance, the image appearing almost as quickly at pounded the great importance of time in the back of the plate as at the front. A development, they gave no further help to bromide in the developer has quite an opposite uniformity in practice than the fact that, effect. The use of a bromide or other restrainer having once developed a plate to a required | in the developer alters the factor. contrast or steepness of gradation, you could The experienced photographer using this attain the same steepness (development factor) timing system will sometimes alter the multiwith another plate by using exactly the same plying factor to bring an exceptionally wide developer, at exactly the same temperature, range of tones in his subject within the limits for exactly the same time. As it is difficult in of his printing process. practical work to ensure an exactly uniform When investigating the laws of appearance, developer (as regards alkali especially), and I found that the ratio of the appearances of all still more difficult to keep an exactly uniform. the various tones in an exposed plate was not temperature all the year, a practical working altered by variations in the character and standard was still wanting. It is this aspect activity of the developer, and that if the times of development to which I have devoted most of appearance of a slip of plate exposed on the investigation.

Hurter and Driffield plan, is plotted out in a In 1893, while testing a large number of similar way to the Hurter and Driffield method plates for speed, and developing them together of plotting out densities, it is possible to read in one dish, I observed that some plates de. the speed of the plate by an observation of the veloped more readily than others, and attained diagram. I have made a recording instrument contrast with greater rapidity ; also that the for observing these appearances, and recordiug image on these plates appeared more quickly them on a diagram, but do not propose to than that on the others. In order to equalise follow up this branch of the subject in this the development, I adopted the plan of develop paper. ing each plate for a fixed multiple of its time To return to the practical question of con. of appearance. In this particular case the trolling results by time of development, I throw time of appearance made correctly the allow on the screen prints from negatives of the same ance due probably to the different character of subject and exposure developed in a 2 grain gelatines used in the emulsions. But this led pyro soda developer, i grain bromide, for 3

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