Lana, who seems to have had no knowledge of the preceding ones; at least he makes no mention of them. The case with Lana was perhaps the same as with many ingenious men, who possess great powers of invention. As they never read, but only think, they are unacquainted with what others have done before them; and, therefore, consider every idea which comes into their mind as a new one. He proposed a harrow, the spikes of which should make holes in the earth, in the same manner as gardeners do with their beanplanter, and the grains of corn were to fall into these holes from a box pierced like a sieve, and placed over the harrow.*

I do not know whether this, at present, could be called a sowing-machine; but it is not improbable that an apparatus of this kind would facilitate the planting, or, as it is termed, setting of wheat, which in modern times has been revived in England, and particularly in Suffolk. For this purpose holes are made three inches apart, in rows, four inches distant from each other, with a bean-planter, by men and women. Each labourer is followed by three children, who throw two or three grains of seed into each hole. One labourer in a second can make four holes, and in two or three days plant an acre. For this he obtains nine shillings, one-half of which is given to the

Prodromo, overo saggio di alcune inventioni nuove, premesso all' arte maestra. In Brescia 1670, fol. p. 96, fig. 26.

children. By these means there is a saving of one half the seed; and this defrays the expenses. The wheat also, when it grows up, is cleaner as well as more beautiful; and this method, besides, affords employment to a great number of persons.

However minute and ridiculous this method of planting may appear to our practical farmers, it is nevertheless true that it has been found beneficial in Upper Lusatia.†

The objection that corn when planted in this manner may throw out too many stems, which will not all ripen at the same time, can be true only when the grains are placed at too great a distance from each other. The German mode of farming, however, is still too remote from horti culture to admit of our attaching great value to the advantages with which this method is attended.

I shall here remark, that Sir Francis Bacon says that in his time, that is, in the beginning of the seventeenth century, attempts had been made to plant wheat, but being too laborious it was again

* See the excellent account of the agriculture in Suffolk in my Beyträgen zur Oekonomie, &c. i. p. 1. It was written by Mr. M. F. Wild, of Durlach, who in the year 1767 was one of my pupils, and afterwards became teacher in the Institute of Education at Colmar. But alas! I do not know whither he has now been swept by the vortex of the Revolution.

+ Leske Reise durch Sachsen. Leipzig 1785. 4to. p. 319.

Neue Abhandlungen der Cellischen economischen Geselschaft, ii. p. 79.

abandoned, though he declares it to be undoubtedly advantageous.* In the most populous districts of China almost all the corn is set, or it is first sown in forcing-beds, and then transplanted.† The English call the labour with the sowing-machine drilling, and the planting of wheat they call dibbling.

MANGANESE.

THE term glass making announces more than the art really performs. In our glass-houses glass is no more made than starch is by those who are called starch-makers. The latter only separate the starch from those parts with which nature had combined them; and our glass-makers merely bring to a state of fusion the glass already produced by nature,, and then form it into vessels of various kinds. As it is, however, not fusible by itself, it requires, before it can be fused in the fire, an addition which, in general, consists of an alkaline salt together with some calcareous earth. Glass-making, therefore, is only a reforming of natural glass; but by these means it always loses in quality. The addition, indispensably necessary, renders it more fragile and brittle, so that it often suffers from the action of the air and of acids. On

Sylva Sylvarum, cent. 5. § 442. p. 267.

+ Algem. Histor. der Reisen, vi. p. 217..

this account the windows of hot houses, and of apartments continually filled with thick vapours, become at length opàke, and the case is the same with glass which has lain for centuries in the earth or in the sea. That play of colours observed on the surface of glass, and which lessens its transparency, announces the commencement of efflo

rescence.

Hence appears the reason why polished rock crystal is so superior to the best crystal glass of our glass-houses. Even an inexperienced eye can immediately distinguish the former from the latter, by its greater brightness and transparency, as well as by its extraordinary splendor. This substance, however, may be reformed also by art, but merely by polishing, and not by fusing, which would be impossible without some addition. Glass-makers who wish to deteriorate their articles in the least degree possible, must use very little addition, and even lessen that which they have employed by exposing their glass a long time to the fire. But it then becomes so difficult of fusion, and tough, that it can no longer be treated in the usual manner. For this reason, those who prepare artificial precious stones, or the best prisms for philosophical experiments in regard to refraction, must anneal the glass, which has become quite stiff, in the furnace; then break it, and form the pieces to the proper shape by grinding them. For common green or blackish-green glass,

any

kind of sand and every kind of siliceous earth, if not too impure, are sufficient; but for white glass,

the purest sand or quartz, as well as the purest alkaline salts, must be selected; and even then the glass will not acquire the most beautiful white colour and brightness, unless some manganese be added to the frit.*

That the art of glass-making may have arisen. from an accident, such as that mentioned by Pliny,† I am ready to admit; but by what accident were artists made acquainted with the use of manganese, a mineral the outward appearance of which seems to announce nothing that could be useful to the glass-maker? It is not found in such abun

* Under this appellation, writers on the art of glass-making understand a mixture of sand or siliceous earth and alkaline salts, which at the German glass-houses, where the above word is seldom heard, is called einsatz. It appears to have been brought to us, along with the art, from Italy, where it is written at present fritta, and to be derived from fritto, which signifies something broiled or roasted. It seems to be the same word as freton, which occurs in Thomas Norton's Poem, Crede mihi sive Ordinale, where it however signifies a particular kind of solid glass, fused together from small fragments. This Englishman lived about the year 1477. His treatise was several times printed. It is to be found also in Mangeti Bibliotheca Chemica, ii. p. 307, a. where the word is thus introduced :

Durior species (vitri) vocatur freton,

Ex vitrorum fracturis id evenit,

Tinctura smaltorum vitriariorum

Non penetrabit illud, ut referunt.

+ Plin. xxxvi. 26. § 25. See Hambergeri Vitri Historia, in Comment. Societ. Gotting. tom. iv. anni 1754. p. 487; an extract from which may be found in Hamburgischen Magazin, xviii. p. 478.