194 



Journal of Applied Microscopy. 



with the front removed. It contains an 

 electro-magnet, E-M, placed in the cir- 

 cuit as described above. The armature, 

 A, is attached to the upper end of a lever 

 L, fastened to the bottom of the box by a 

 hinge and free to move through a small 

 arc whose length is varied by the adjust- 

 ing screw, S. On the same side as the 

 armature, but lower down so as to afford 

 a good leverage, is a small rubber 

 cushion which shuts against and closes 

 the main inlet tube when the armature is 

 drawn to the magnet. A smaller pilot 

 inlet regulated by the gas cock affords 

 gas sufRcient to maintain a pilot flame 

 when the main inlet is closed. These 

 inlets and exit are short metal tubes and 

 are connected with the gas supply and 

 with the burner by means of rubber tub- 

 ing. While the circuit is open the gas 

 enters at the main and pilot inlets and 

 passes out at the opposite side of the box 

 to the burner. When the circuit is .closed 

 by the mercury rising in the bulb till it 

 touches the electrode at E, the main inlet 

 is shut off and the pilot inlet admits gas 

 suflficient only to preserve the flame till 

 the oven cools and the circuit is inter- 

 rupted by the fall of the mercury. The 

 temperature at which the circuit is made 

 and broken may be regulated by raising 

 or lowering the wire in the neck of the 

 tube. The coils of the electro-magnet 

 are wound with No. 32 copper wire and 

 have a resistance of one ohm each. Two 

 Edison-Leland cells are sufRcient to oper- 

 ate the regulator. 



This in an improvement upon the old 

 arrangement where the gas was confined 

 to an outer and an inner tube, with a 

 magnet working on a membrane over the 

 ends of the tubes, because the expansion 

 of the gas in the box prevents the too 

 sudden lowering of the supply at the 

 flame, which occurred under the eld 

 plan, and also because there is no mem- 

 brane to get stiff or crack. 



DONALDSOX BODINE. 



Wabash College. 



Projection Microscope — A New 

 Departure. 



At the annual meeting of the Ameri- 

 can Microscopical Society, Prof. M. C. 

 White, M. D., of Yale University, ex- 

 hibited an electric lantern microscope 

 with a 20 mm. objective with an esti- 

 mated aperture of 0.95 n.a., manufactured 

 on his order on the following principle: 



Taking as a model the 5 mm. apochro- 

 matic objective of Bausch & Lomb cata- 

 logue, made on the formula of Prof. 

 Hastings, Prof. White dit-ected Bausch 

 & Lomb to make an objective which 

 should have the diameter of every lens 

 and the radius of every curvature four 



times as great as that of the 5 mm. 

 apochromatic objective. Prof. White 

 desired to try such a mammoth objective 

 in the projection microscope. 



The objective thus made is shown of 

 natural size in Fig. 1, and is seen com- 

 pared with aa. achromatic of Zeiss 0.30 

 n.a., of the same powers as the large ob- 

 jective, and on the other side is shown 

 the 12 mm. 0.65 n.a. apochromatic made 

 by Zeiss. 



In Fig. 2 is shown, half natural size, the 

 new objective in the carrier made as for 

 a lantern objective. Beside it is also 

 shown a No. 1 projection eyepiece made 

 for use in the microscope with this new 

 objective. This new projection micro- 

 scope, hastily put together in temporary 

 mountings, not yet perfected and only 

 partly tested, was shown by Dr. White, 

 showing blood corpuscles well defined 

 on the screen. 



A vote of thanks was tendered to Dr. 

 White by the society for exhibiting this 

 new and expensive apparatus, which 

 bids fair to greatly increase the useful- 

 ness of the projection microscope. 



Dr. White's theory is that if, in using 

 the ordinary microscope, a certain angu- 

 lar aperture is required to secure proper 

 definition with a magnifying power of 

 1,000 diameters, -then a similar aperture 

 will be necessary to secure good defini- 

 tion in an image projected on the screen, 

 even if it is obtained with a three- 

 fourths-inch objective and a projection 

 eyepiece. 



Fig. 4 shows this new projection mi- 

 croscope as mounted for use. It is sup- 

 plied with J. B. Colt's Criterion lantern 

 electric light, with rheostat taking incan- 

 descent current of 110 volts and reduc- 

 ing it to 17 volts. The arc light of the 

 carbons is passed through condensers 

 and then cooled by a three-inch cell of 

 water or alum. The microscope part as 

 shown has a mechanical stage with 

 substage and achromatic Abbe Con- 

 denser of 1.00 n.a. The body of the mi- 

 croscope is three inches in diameter and 

 twelve inches long between the mount- 

 ings of the objective and eyepiece. The 

 stage is movable in two directions, also 

 may be advanced or receded by rack and 

 pinion, and also by a fine movement for 

 accurate adjustment of focus. The ob- 

 jective also has a movement of one inch 

 by rack and pinion, and the drawtube 

 furnished with rack and pinion move- 

 ment may be extended three inches as 

 a drawtube is extended in the ordinary 

 microscope. 



Insects may be killed with parts fully 

 extended by throwing them into hot 

 water or hot solution of corrosive subli- 

 mate. 



