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 horticulture 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 œconomischen 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 name 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 opake, 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 effo rescence. Hence appears the reason why polished rock crystal is so superior to the best crystal glass of our glass-houses. Even an unexperienced 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,t 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 Bibliocheca Chemica, ii. p. 307, a. where the word is thus introduced: Durior species (vitri) vocatur freton, Ex vitrorum fracturis id evenit, 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. dance as to allow us to suppose that it naturally presented itself; nor do we know that any older application of it may have induced the ancients to employ and examine it in such a manner that the present use of it might be accidentally discovered. In general, it resembles son:e kinds of iron-stone, which it was considered to be till a very late period. That iron, however, colours glass must have been very early remarked; and therefore it could occur to no one to employ manganese for depriving frit of its colour. It produces this decoloration only when it is added sparingly, and according to a determinate proportion; otherwise it gives to the glass a violet colour, something similar to that of the amethyst. The application of manganese was certainly taught by accident, and not by theory. But in regard to the question, why it frees glass from its dirty colour, it must be admitted, if we readily acknowledge the truth, that we can offer only hypotheses; as the old chemists called in the aid of phlogiston, and the new that of oxygen. Did a false hypothesis, then, conduct to this discovery? That this was the case, has been aserted by old as well as more modern writers, and is no doubt possible. Thus Kepler, from an erroneous hypothesis in regard to the revolution of the planets, discovered the ratio of their motion, according to their distance from the sun; and such instances may be adduced in favour of hypotheses which have |