ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



329 



or balance witliout any appreciable interference with temperature. 

 The glass vessel is provided with a pierced cover or shade, and a 

 little stream of water of a uniform temperature may be kept flowing 

 through the vessel. 



By means of a " chromozone " battery, supplied by Mr. 0. March, 

 it has been found, at the Standards Office, that a light may be main- 

 tained at an insignificant cost for fifty hours without, of course, any 

 attention. During a recent comparison made by Mr. Chaney of two 

 standard kilogram weights it became necessary to use the lamp, but 

 the action of the balance was not interfered with by the proximity of 

 the lamp, the probable error of the result being only ± 0*005 mgr. 



Standard Thickness of Glass Slips.* — E. M. Nelson suggests that 

 it would obviate much inconvenience where immersion condensers are 

 used, if a standard thickness was adopted for glass slips. At present 

 there are so many thicknesses in use that it is sometimes very trouble- 

 some to adjust the focus properly with high powers, as if too thin the 

 drop will not adhere, and if too thick it gets squeezed out. He 

 proposes that a thickness of 1/20 in. should be adopted as the best 

 standard, and " if every person would buy slides of that gauge only, 

 the thing might easily be done." 



Mr. A. D. Michael said, at the meeting at which this suggestion 

 was made, that he thought he should find a standard gauge for 

 glass slips a great nuisance, especially for such objects as required 

 the use of high powers ; while Dr. Carpenter thought it might be 

 well to try to get some uniform slip for use with oil-immersion 

 objectives. 



Rabl's Slide for Viewing Objects on both Sides.j — C. Eabl 

 describes a slide (fig. 81) which he found useful in his researches on 

 cell-division. It consists of two pieces of glass a h (thick lines), 



Fig. 81. 



with two strips c d, and two square pieces e /, cemented on so as to 

 form a frame of glass surrounding a central space. A piece of thin 

 glass (shown by dotted lines) is cemented beneath, on which the 

 object is placed, and when a similar piece is placed over the object it 

 can be examined on either side with the highest powers. 



* Joum. Quek. Micr. Club, ii. (1885) pp. 120-1. 

 t Morphol. Jahrbuch, x. (1884) pp. 218-9 (1 fig.). 



