324 



SUMMABY OF OUBRENT RESEARCHES RELATING TO 



The above quotation shows that the author, at the time he wrote, 

 had not merely not seen the paper of the German student but had 

 not the most elementary appreciation of the manner in which 

 hexagonal markings are derived from six spectra. The statement 

 that the " purely mathematical result is a very simple business," 

 &c., is as wide of the actual fact as the version of Mr. Stephenson's 

 paper. 



These are not by any means all of the mistakes into which the 

 author has, no doubt unwittingly, fallen. It is, we venture to think, 

 unfortunate to say the least that such crude notions should be hurried 

 into print without any care having been previously taken to master 

 the elements of the subject supposed to be treated of. 



lUuminatioii by aid of Air-bubbles.* — For very delicate struc- 

 tures, such as fur-fibres, Mr. H. L. Brevoort often purposely permits 

 air-bubbles in the mounting material, or introduces them into it. 

 The chances are that some of the fibres will pass through some of the 

 air-bubbles, and when they do this in the proper position, the fibres 

 will be found to be illuminated by the reflection of light from the 

 upper part of th§ concave surface of the bubble, and the surface of 

 the fibres may be studied with a 1/16 in. immersion lens as readily 

 as with a 1 in. This method of illuminating he finds of great service 

 with the highest powers, and has used it with balsam and glycerin. 

 With the latter it works exceedingly well. The air-bubbles may best 

 be introduced by means of a stylographic pen-filler. 



Campbell's Fine Adjustment.t — Mr. E. M. Nelson describes a fine 

 adjustment devised by the Eev. James Campbell, which he considers 

 particularly suitable for Microscopes of the Continental type, where 

 direct-acting screws are employed. The device 

 consists essentially of a differential screw-adjust- 

 ment, and is shown in fig. 61 as made by Messrs. 

 J. Swift and Son. 



D is the milled head of the direct-acting 

 screw. The upper part S of the screw has 20 

 threads to the inch, and the lower part T 25 to 

 the inch. B is the fixed socket forming part of 

 the limb of the Microscope, and H is the 

 travelling socket connected with the support of 

 the body-tube. The revolution of D causes the 

 screw-thread S to move up or down in B at the 

 rate of 20 turns to the inch, whilst the screw- 

 thread T causes the travelling socket H to move 

 in the reverse direction at the rate of 25 turns 

 to the inch. The combined effect, therefore, of 

 turning D 20 revolutions, is to raise or lower T 

 and with it the body-tube 1/5 of an inch, or 1/100 in. for each 

 revolution. The spiral spring below H keeps the bearings in close 

 contact. 



• Joum. New York Micr. Soc, i. (1885) p. 203. 

 t Engl. Mech., xlii. (1886) p. 443 (1 fig.). 



