342 



SCIENCE, 



[N. S. Vol. XXIV. No. 611. 



differs strikingly from any marten skin in 

 the museum collection, or elsewhere, so far as 

 I am aware. The long- bristly hairs are every- 

 where lacking on the skin, which bears about 

 the same relation to a normal marten that a 

 plucked beaver or seal skin does to an un- 

 plucked one. Coues^ describes the pelage of 

 the marten as consisting of three kinds of 

 hairs : 



The first is very short, soft and wool-like * * * 

 the second soft and kinky, like the first but very 

 much longer, coming to the general surface of the 

 pelt. The third is the fewer, still longer, glossy 

 hairs, bristly to the roots. 



The specimen in question entirely lacks the 

 long glossy hairs, and possesses a very few 

 only, of Coues's second variety of hairs, with 

 soft kinky base and short bristly tip. The 

 entire pelage is practically composed of the 

 soft short underfur. The general color of the 

 skin is not abnormal; the head, chest, legs and 

 feet are perhaps a little darker brown than 

 the usual run of skins. The general size and 

 proportion of the skin differ in no way from 

 that of a normal marten. 



Marcus W. Lyon, Jr. 



an object-finder for the micro-projection 

 apparatus. 



No doubt every one who has undertaken to 

 project the image of a microscopic preparation 

 directly upon a screen for class or lecture 

 demonstration purposes has realized the diffi- 

 culties in the way of rapid and accurate loca- 

 tion of the exact part of the object desired. 

 Indeed, this method of illustration is at pres- 

 ent seldom made use of, owing chiefly to the 

 great loss of time involved, and to the dis- 

 tracting effects upon the attention of the class 

 or audience. 



Some time ago the writer devised an attach- 

 ment for the micro-projection apparatus which 

 so effectually overcame the difficulties men- 

 tioned above as to render this method of dem- 

 onstration quite as expeditious and precise as 

 that with ordinary photo-micrographic or 

 other lantern slides. With this condition as- 



^ ' Fur-bearing Animals,' U. S. Geol. Survey, 

 Miscell. Pub., No. VIII.. 1877, p. 82. 



sured, the advantages of the method are ob- 

 vious. Inquiries regarding this apparatus 

 have led to the belief that the publication of 

 a description of it may be worth while. The 

 following description and the accompanying 

 figures represent the latest improved form of 

 the attachment. 



As indicated in the figures, this attachment 

 consists of a rotary object stage and a sec- 

 ondary, short-range projector, mounted on the 

 same base-board with the usual projection 

 apparatus. The light is taken from the elec- 

 tric arc, or other illuminant, L, of the main 

 projector, through the opening at the side of 

 the hood. In place of the blue or purple glass 

 commonly found in this opening, there is put 

 a simple coUimating lens. The parallel 

 emergent rays are reflected by the mirror. A, 

 into the line of the optical axis of the finder, 

 which is parallel to that of the projector 

 proper. By means of the condenser, B, these 

 rays are brought to a focus at the position 

 of the object on the revolving stage C. A 

 good hand lens at D projects an image of the 

 object upon the small screen, E, which need 

 not be more than about thirty inches from the 

 object. The plan of the base-board, Fig. 2, 

 will make clear the arrangement of the parts. 



Fig. 3 shows the plan of the rotary stage- 

 plate, with four openings and spring clips for 

 holding the slides- in position. Fig. 4 repre- 

 sents a face-view of the screen, E, which has 

 a dead-white surface, with the two centering 

 lines in black. All the parts are mounted on 

 telescoping pillars, and are made adjustable 

 in position on the base-board. 



The rotary stage-plate requires special care 

 in its construction and mounting, as it must 

 be both accurate and rigid. Fig. 5 shows the 

 details of the mounting. On top of the heavy 

 pillar is the sleeve, made from thick-walled 

 brass tubing. On the ends of the sleeve are 

 the two collars, l> and c. Working in the 

 sleeve is the shaft, which is held in position 

 by the collar a and the nut n. The plunger, 

 p, actuated by the spring, s^ passes through 

 the collars, h and c, and engages the collar a. 

 Four holes are drilled in the collar a for the 

 plunger, and these holes must be exactly 



