292 SUMMARY OF CURRENT RESEARCHES RELATING TO 



camera from wliicli the objective has been removed ; and the author suggests 

 its employment to demonstrate the phenomena of electrolysis (fig. 40). 



A A are mercury connections which receive the wires from a battery of 

 six small Grove's cells ; a rheostat, contact-breaker, and commutator being 

 included in the circuit. The current is conveyed from A A by a a to B B, two 



vessels of mercury, which are insulated and fixed upon C a plate with a hole 

 in its centre, which rests upon the stage. D is the object-carrier, on which a 

 drop of the solution is placed, being then covered with a flat watch-glass E, 

 having its convex side downwards ; the electrodes are formed by the wires 

 e e, terminating in arrow-shaped platinum points, which are brought into 

 contact with the drop. Any desired movement is given to the object by the 

 motion, not of D, but of the plate C. The mercury connections obviate the 

 pressure or elasticity which would be introduced by solid connections. 



Nelson's "New Student's Microscope."— Mr. E. M. Nelson claims* 

 that this instrument " begins a new era in the progress of ' microscopy,' " 

 and that for the " first time in the history of the Microscope a thoroughly 

 sound full-sized instrument " can be supplied at the same price as a 

 student's Microscope. 



Eeferring to some of the points adopted in this new Microscope — points 

 where there must of necessity be much that is old in design — Mr. Nelson 

 divides Microscope feet into four classes: — 1st. The simple tripod, illus- 

 trated by the Powell form. 2nd. The plate and uprights. A flat plate with 

 pillar or pillars, as in the Beck model ; and a plate with flat uprights, as in 

 the Andrew Koss. 3rd. The bent claw, a very common and bad form, used 

 by many makers. 4th. The heavy horseshoe, the usual Continental model. 

 The plate and uprights, though a good form, was not adopted because it 

 was too heavy and expensive. The bent claw is a bad form : it is heavy, 

 easily capsized, and while seemingly a tripod, often rocks on four points. 

 The heavy horseshoe which, until lately, was always fitted to students' 

 Microscopes, has nothing to recommend it. A designer, Mr. Nelson con- 

 siders, " must indeed be hard uj) for resources who can only obtain steadiness 

 by weight. There can be no question but that the tripod in its simplest 

 form is the best. Of all the ways of utilizing it, that adopted by Messrs. 

 Powell and Lealand is the most efiicient, viz. of hanging the Microscope in 

 a horseshoe, supported by three legs ; but that for this class of instrument 

 was quite out of the question, fur cost immediately puts it outside the 

 category of students' Microscopes. 



There is a great difterence between the steadiness of a Microscope 

 perched up on the top of its trunnions, and one that is hung in a tripod. 

 The new Microscope (fig. 41) is placed in a kind of stirrup hanging from 

 the trunnions. . . . The body is large enough to take Zeiss's full-sized eye- 

 piece, viz. 1| in., and is 10 in, long when the draw-tube is pulled out to a 

 mark. When the draw-tube is pushed home, the length is 6*3 in., or 

 Continental gauge. It, therefore, will suit both kinds of apochromatics. 

 The optic axis of the instrument, when in a horizontal position, is 8^ in. 

 from the table. It has rackwork coarse-adjustment, and Campbell's fine- 



* Cf. Eng. Mecli., xliv. (1887) p. 497. 



