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duced more than a few degrees below its mean temperature, yet it is obvious that the diminution must continue till the surface again approaches the temperature of the interior. This equilibrium will take place towards the middle of March, as the surface of the earth is generally within a few degrees of the mean annual temperature. It is found accordingly, as might be expected, that the temperature of the interior as indicated by the pump water is actually a minimum about the middle of March. From that period it gradually increases, and appears to reach its mean about the middle of June. The rain and dews, however, of the succeeding months, being still at a comparatively high temperature, communicate additional caloric to the strata beneath, and must continue to do so till the surface of the ground again descend towards the temperature to which the interior has risen. This point, for the reason already mentioned, will be a few degrees above the mean, and of course the equilibrium ought to take place about the beginning of October, as the temperature of the atmosphere is then generally within a few degrees of the mean annual temperature. It is obvious, however, that the ground, to the depth of several feet, may, from the accumulation of the sun's rays, be preserved at a higher temperature than the mean, even after that of the atmosphere has sunk considerably lower. This will happen perhaps to a certain extent every year, but especially in warm and dry seasons. Making an allowance, therefore, for this circumstance, the equilibrium between the surface and the interior may be expected to take place about the end of October, which agrees exactly with observation, the pump water being then a maximum. From this period the temperature decreases, and reaches its medium again towards the end of December. Besides the coincidence between the above theory and the general results of observation, it is further confirmed by several circumstances of a more particular nature. During the whole of the month of August (1815), when the rain that fell was wholly consumed by evaporation, and of course could contribute nothing to springs, the temperature of the well was stationary at 46.8°. In the course of September, and the first 15 days of October, when the quantity of rain considerably exceeded the evaporation, the temperature rose to 47.8°, being 1o in an interval of about 50 days; and between the 15th and 25th of October, during which time there fell upwards of two inches of rain, with little evaporation, it rose to 48.8°, being 1° in about one-fifth of the preceding interval. It may be inferred that, had the last fall of rain taken place sooner, the pump water would have sooner reached its maximum. But might not the truth of the whole theory be put to the test of experiment, by noting the temperature and quantity of rain, ascertaining as nearly as possible the density and depth of the strata through which it passes before being conveyed to the pump, and determining by calculation the quantity of caloric which it ought to abstract from, or communicate to, these strata? And if

the theory be found to hold in all cases, modified perhaps by the nature of the ground, and other circumstances, will not some correction be necessary in determining the temperature of any place from a single observation of spring water, unless when that observation has been made about the middle of winter or the middle of summer?

Rose-Bank, March 9, 1816.

SIR,

ARTICLE VI.

Description of the Bird Fly. By M. W. Carolan.

(To Dr. Thomson.)

THE history of those insects which infest other animals is a curious subject of investigation, and includes no small branch of natural history. Amongst the varieties of this description, there are few which exhibit a more striking fitness for their situation than the fly which lives upon some birds, and may be often observed upon the partridge and swallow. This fly, like most others, seems to live principally upon animal perspiration, or any thing in a putrescent state; but as it could not get at the cuticular pores of birds without going through the feathers, it is exactly formed for that purpose.

It is rather larger than the common fly, of a clear tea-green colour, and is seldom seen but upon birds. It is quite flat, so that both its body, head, and legs, apply closely to any plain surface on which it may rest. It is very hard, and not easily crushed or killed. Its legs are very strong, and it can move in all directions; and, what is curious, runs with most rapidity sidewise, and does not seem to run easily straight forward. Its flatness, strength, and polished smoothness, without any hairs upon its body; enable it to move with ease among the feathers, and particularly its capacity of running sidewise, which gives it the power of going round the body of the bird beneath the feathers; for the feathers of birds are so placed in transverse rings that no insect, except it were almost invisible, could go straight forward under them. It sometimes appears above the plumage to enter in at a new place, which it performs with great ease and quickness, and without discomposing a single reed of the feathers.

These may seem necessary to preserve the health of some animals, by continually removing the perspiration that would otherwise be lodged about the feathers; and may perhaps act at the same time as a kind of stimulant to the skin. Although there are seldom above two or three on a small bird, yet from their size they must remove a great deal of what is excreted by the skin, as they appear seldom

to leave the bird they live upon, and even remain after the bird is dead. How far does the complete perfection displayed even in the simplest and meanest parts of creation baffle our comprehension, both with respect to their mechanism and utility, and evidence the hand that formed them!

M. W. CAROLAN.

ARTICLE VII.

Description of a new Blow-Pipe. By H. I. Brooke, Esq,

DEAR SIR,

(To Dr. Thomson.)

I SEND you enclosed a drawing of a blow-pipe which I have lately had made upon a principle I believe entirely new in its application to this instrument, and which I have

reason to believe, from the power which it possesses, and the facility with which it may be used, is an improvement upon any that has preceded it. The occasion of my having it made was to relieve the great inconvenience I felt in using

the common blow-pipe with the mouth. The first idea that suggested itself to me was to produce the jet of air from a sort of artificial mouth, or moveable receiver, of rather large dimensions, the capacity of which should be capable of gradual reduction by means of a spring; but it immediately occurred to me that the elasticity of the air itself, if forced into a fixed receiver, would be more uniform in its action than any spring, and might be regulated so as to produce a continued and more uniform jet. I accordingly applied to Mr. Newman, in Lisle-street, to make one upon this principle, to consist of a copper or iron vessel, into which the air is forced by a small condensing syringe, and from which it is suffered to escape through a tube of very small aperture, regulated by a stop-cock; and I have found it capable of affording a very intense and regular degree of heat. The form given in the drawing has been adopted by Mr. Newman for the convenience of packing into a small case; and he has also added to the syringe a screw, by means of which the receiver may be filled with oxygen or any other gas, which renders it more extensive in its application to chemical purposes, and probably so as to supersede the use of the common gazometer. I am, dear Sir, your obedient servant, H. I. BROOKE.

Keppel-street, April 8, 1816.

ARTICLE VIII.

An Account of a Trial of Dr. Reid Clanny's Lamp in some of the Newcastle Coal-Mines. By W. Reid Clanny, M.D.

(Read before the Royal Society, Dec. 7, 1815.)

ON May 20, 1813, a paper of mine, on the means of procuring a steady light in coal-mines without the danger of an explosion, was honoured by a reading before the Royal Society, and accordingly I consider myself as in some measure pledged to lay before that Learned Body the following particulars, in continuation of the subject.

Since the above-mentioned time, explosions in this district have become more frequent, as may be readily understood by comparing the subjoined list with that of my former statement, inserted in the Philosophical Transactions for 1813.

By the falling of a stone from the roof of the mine, an explosion took place in the Hall Pit, at Fatfield, Sept. 28, 1813; by which 32 persons were killed, and, four wounded. Three other explosions occurred in that mine at different times, by which three men were killed.

Upon Dec. 24, 1813, another explosion occurred at Felling; by which 23 persons were killed, and 21 much wounded.

The Hebburn Colliery exploded upon Aug. 12, 1814; and 11 men were killed, leaving nine widows and 27 children in the greatest distress.

An explosion at Leefield Colliery upon Sept. 9, 1814, killed four men, who left two widows and 12 children.

June 2, 1815, the Success Pit exploded; by which 54 were killed upon the spot, two were suffocated, and 15 very severely wounded, some of whom afterwards died.

The Tyne Main Colliery exploded upon June 5, 1815; by which one man was most severely scorched.

July 27, 1815, the Sheriff Hill Pit exploded; by which 10 men and boys were killed.

By some persons concerned in coal-mines it has been asserted that by ventilation, properly conducted, explosions may be avoided. I grant that by proper ventilation several calamitous accidents might in all probability have been prevented; but it may be fairly asked where those coal-mines are which may be said to be properly ventilated? As a case in point, the catastrophes at Felling Colliery may be instanced. In 1812 this colliery was understood to be one of the best ventilated and best regulated coal-mines in this district; yet on May 25, in that year, 92 persons were killed by an explosion; and 19 months afterwards, as stated above, though incredible pains and expense had been bestowed upon it by the humane

proprietors, an explosion occurred, by which 23 persons were killed, and 21 severely wounded.

Many of the old coal-mines are upon such a bad plan of ventilation, that the talents of the first viewers and engineers are insufficient to keep them working, whilst the poor pitmen are harassed with continual fears of destruction.

In this district there are several coal-mines that have only one shaft, which serves the double purpose of ventilation and working. In a considerable number of collieries there are immense collections of carbureted hydrogen gas, which have been accumulating in several instances for many years, without the smallest chance of its ever being carried out of the mine. Under these and similar circumstances, need we be surprised at the increased frequency of explosions?

In my former paper some of the principal causes of explosions were described; and it may perhaps be acceptable to mention some others, with which I have lately become acquainted.

1. The great extent of collieries, and the incertitude which often prevails as to their boundaries, from the neglect of those immediately concerned, in not making correct maps and accurate records.

2. When the plan of the colliery is lost, or abstracted.

3. When sudden eruptions of carbureted hydrogen gas unexpectedly mix the whole circulating mass of air up to the firing point.

4. When the barometer stands below 29°, and the wind is at S. E., the atmospheric current becomes too light to sweep off the increased discharge of inflammable air which then issues out of every part of some mines.

5. When the inflammable air prevails between the workmen and the upcast shaft, and a fall of stone from the roof, or other causes, occur to force back the atmospheric current towards the downcast shaft.

About four years ago I constructed a small lamp of a strong glass, the bottom of which was shut, with the exception of a small opening to admit the tube from the bellows, for throwing in the necessary quantity of air to support the combustion of the candle within the lamp.

I found that it safely insulated the candle; but I was soon told that it would never answer for the purpose intended; that frequently large pieces of stone fell from the roof, which would destroy the lamp; and as the candle would thereby come in contact with the mass of inflammable air of the mine, an explosion would occur as a matter of course. I also found that valves would not suit; for the expansive force of the explosions within the lamp threw open the valves, and allowed a communication to take place between the candle and the surrounding atmosphere; besides, the water, when used as a valve, not only keeps the apparatus cool, but ensures

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