ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 507 



" Note that when (1) the wheel G is locked against rotation by the 

 cam-wheel E resting on the points of the long teeth, and is released and 

 moves forwards or backwards when the lug F engages with the short 

 teeth H. (2) The wheels E and D are rigidly fixed on the same arbor 

 and revolve together. The wheels C D E G are mounted in a straight 

 line on the frame, but for illustration purposes only ; E and G have 

 been separated from C and D to avoid any overlapping of E and D in 

 the diagram." 



Composition of Brass.* — The question asked by " Theodolite," 

 What is brass ? opens up an interesting and important subject to 

 Microscopists. It is said that many modern Microscopes wear out iu a 

 very short time, in spite of their having adjusting screws to take up the 

 wear, that the slides and V-grooves wear and the threads of screws strip, 

 so that in a very little time the instrument becomes useless. From 

 " Brassf ounder's " communication it would appear that the modern 

 Microscope is, like other scientific instruments, made of inferior or too 

 soft metal. This writer says : — " When I was an apprentice brass was 

 copper and zinc in different proportions, according to quality, with the 

 addition of a little tin for the best metal ; but cutting prices in com- 

 petition have altered this, so that modern brass is any mixture of metals 

 which will produce a yellow surface when polished. The introduction 

 of automatic machines in the instrument trade is, however, very largely 

 responsible for bad metal in instruments. Really good, age-lasting brass 

 is very tough in working up ; it is also rather hard. Owing to the way 

 in which it pulls on to the tools in working, it becomes very hot, and 

 has to be worked at a low speed. The brassfounder gets over the 

 difficulty by mixing a metal which will work well in the machine, and it 

 happens that a crisp, cool-cutting metal is very poor in quality. Good 

 metal will stand nearly a white heat before melting, but the metal usually 

 used will not stand the ordinary heat required for brazing. 1 ' 



Several other contributors write on this subject, and give the com- 

 position of various kinds of brass ; for these the original may be con- 

 sulted with advantage. 



B. Technique.! 



(1) Collecting Objects, including: Culture Processes. 



Cultivation of Algae.J — -C. Sauvageau takes small fragments of 

 plant, and having cleaned and washed them, places them in a drop of 

 filtered water in a Van Tieghem's moist cell. For the observation of the 

 reproductive bodies the thinnest slips are, of course, the best. If it be 

 proposed to follow the course of the germination, thicker slips are 

 preferable. Ordinary slides are too smooth for the later stages of 

 development, as the young plantules adhere badly and undergo abnormal 



* English Mechanic, April 3, 10, 17, 24, May 1, 1908. 



t This subdivision contains (1) Collecting Objects, including Culture Pro- 

 cesses ; (2) Preparing Objects ; (3) Cutting, including Imbedding and Microtomes ; 

 (4) Staining and Injecting ; (5) Mounting, including slides, preservative fluids, etc. ; 

 (6) Miscellaneous. 



% OB. Soc. Biol. Paris, lxiv. (1908) pp. 700-1. 



