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HARDWICKE'S SCIENCE-GOSSIP. 



[Aug. 1, 1868. 



MICROSCOPY. 



Diatom-type Slide. — At the last meeting of the 

 Quekett Microscopical Club (June 26th) an object 

 was exhibited which proved a great attraction. 

 This was Holler's "Diatomaceen Typen Platte," 

 one of which had been sent from Prussia for exhi- 

 bition to the members, through the kindness of 

 Herr Weissflog, of Schoenebeck. It is an ordinary 

 3 by 1 inch glass slide, with the objects in the centre 

 occupying a square about the eighth of an inch in 

 diameter. This square consists of four smaller 

 squares each containing about 100 diatoms arranged 

 in parallel lines and consecutive order, so that the 

 slide contains 400 diatoms belonging to 370 species, 

 types of the genera and subdivisions. This is there- 

 fore a slide of the typical forms of Diatomaeese, 

 the key to which is a book which accompanies it, 

 and in which the name of each diatom, according to 

 its line and its position upon that line, is easily 

 found. As an example of microscopical mounting, 

 it was regarded as a marvel of ingenuity and per- 

 severance, some of the species being represented by 

 a side and a front view. The great problem appeared 

 to be how it could have been accomplished, how 

 the straight lines were invariably maintained, how 

 such very minute objects could have been arranged 

 to the number of 400 in consecutive order, and then 

 covered without the fracture or displacement of a 

 single frustule. The price at which they are 

 supplied by Mr. J. D. Moller, of Wedel, in Holstein, 

 viz., three pounds sterling, is not large when the 

 labour of production is taken into account. Other 

 slides of diatoms and other objects by the same 

 manipulator, we have examined, and consider them 

 good and cheap ; let us hope that this will be one 

 inducement for British microscopists to cultivate a 

 better acquaintance with their continental neighbours 

 and fellow-workers. 



Silkworm Disease. — The terrible suffering that 

 has been caused in the south of France by the 

 disease which has attacked the silkworms for the 

 last twenty years— it made its appearance in 1848— 

 has drawn the attention of scientific men to the 

 subject, and M. Pasteur, the great authority on 

 ferments, has taken up the subject. He is of 

 opinion that the value of the eggs, or seeds (graines, 

 as the silkworm's eggs are called in France), may 

 be tested by means of the microscope, and he has 

 published a clear account of the appearance pre- 

 sented by the sound and diseased eggs. Several 

 proprietors and others have tried experiments with 

 eggs thus selected with marked success. Amongst 

 others, M. Henri Mares, of Montpclier, who has 

 an immense breadth of land under vines in the plain 

 of Launac, near Frontignan, and to whom France is 

 indebted for the application of sulphur as a pre- 

 ventive of the oidlui/i or vine disease, has tested 



M. Pasteur's plan on a considerable scale. Before 

 the middle of May, many of the worms had under- 

 gone all their transformations, and some few were 

 busy spinuing their cocoons ; they looked perfectly 

 healthy and were of great size, and everything 

 promised well for the experiment. The fact must 

 not, however, be overlooked, that the fine appearance 

 of the worms cannot be attributed to the selection 

 of the eggs alone ; M. Mares' lofts are well supplied 

 with mulberry leaves, and kept carefully clean ; the 

 experiment is, in short, carried on by a man of high 

 education, scientific attainments, and active habits, 

 and thus the causes of success are double, — micro- 

 scopic selection of eggs and sanitary arrangement. 

 The poor silkworm-breeders generally present a 

 very different spectacle; their chambers are kept at 

 a great heat, without any careful arrangement 

 against draughts, while the supply of food and the 

 cleansing often suffer from want of sufficient hands 

 to carry the operations out properly. M. Mares is 

 not of opinion that the stripping of the mulberry- 

 trees causes the leaves to lose their value as food 

 for the worms ; his trees are reduced to bare poles 

 during the season, and yet they present a most 

 vigorous appearance. It is to be hoped that the 

 efforts of the government, aided by men like M. 

 Pasteur, M. Guerin Meneville, and M. Mares, will 

 soon eradicate the silkworm disease, which has cost 

 France and other countries so many millions. — 

 Journal of the Society of Arts, June 5th. 



Pocket Finder. — A very convenient and useful 

 little instrument is made by Mr. E. Wheeler, of 

 Holloway, which is, in fact, a pocket miscroscope. 

 It consists of a tube about four inches in length, and 

 less than three-fourths of an inch in diameter, 

 with a Huyghenian eye-piece, and a triplet 

 (objective) of about half an inch power. A 

 movable cap bearing a plain glass disc slips 

 over the objective, and when it is desired to test 

 a gathering of Diatoms or Desmids, a little is 

 placed upon the glass disc and the cap drawn out- 

 wards, until the object is in focus. For all practical 

 purposes it is sufficiently powerful for field-work, 

 will really go into the waistcoat pocket, and costs 

 about a guinea ; so that it is efficient, portable, and 

 cheap. We commend it to the attention of all 

 collectors of microscopical objects and field- workers. 



Maple Blight. — Since writing the notice of this 

 fungus at page 136, we have received specimens 

 from the United States, and upon examination con- 

 sider them to belong to the same species (Uncinula 

 bicornis, Lev.) notwithstanding, that the tips of the 

 appendages are not divided, but simply recurved, 

 in a circinate manner. Dr. Leveille remarks that 

 the specific name is not a good one, since the 

 appendages are sometimes simple, and sometimes 

 forked. Our American specimens are on Maple 

 leaves from South Carolina. 



