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V. — On a New Micrometric Goniometer Eye-piece for the 

 Microscojye. By J. P. SouimvoRTH. 



After a few experiments by Dr. H. T. Porter and myself, we have 

 succeeded in making an eye-piece micrometer and goniometer which 

 equal in accuracy and surpass in simplicity and cheapness any we 

 have seen, and we have used those of some of the best makers in 

 this country. The objection to the eye-piece micrometers in use 

 is the want of boldness in the division lines, which makes them 

 fatiguing and hurtful to the eyes. To overcome this objection we 

 were led to experiments in making micrometers by the aid of photo- 

 graphy, which have resulted in success. The steps of the process 

 are these : — 



1st. A scale of 100 heavy India-ink lines of about |^th of an 

 inch apart is drawn on a dead-white surface of Bristol board. The 

 lines marking every ten divisions are 6 inches long, and extend 

 1 inch each side of the scale ; those marking every five divisions 

 are 5 inches long and extend one-half inch beyond the scale ; the 

 remaining lines are 4 inches long. 



2nd. By photographic process for copying engravings, a negative 

 is taken, on which the scale equals about 2 inches in length, and is 

 intensified by mercuric chloride and potassium cyanide. 



3rd. With a copying camera and lens for taking transparent 

 positives for the magic lantern, a transparent positive of this nega- 

 tive is taken on micrometer glass, reducing the scale to the length of 

 one-half inch. In this the lines are a^o^h of an inch apart. After 

 intensifying, washing, and drying, a cover of thin glass is cemented 

 on with Canada balsam, and the slide cut to fit the slit in the 

 micrometer eye-piece. It can be also mounted with a spring and 

 micrometer screw, hke Jackson's micrometer. In oui* micrometer 

 the hnes appear to stand out in rehef, and are jet black, while the 

 spaces between them are translucent enough to admit of the accurate 

 measurement of the details of minute algae and fungi to the 

 iT's^oo^th of an inch, 



Eegarding the goniometer : — 



1st. A circle about 18 inches in diameter is drawn with India- 

 ink, divided into degrees. The centre is indicated by a dot, and one 

 diameter is drawn. Every 5 and 10 degrees are indicated by 

 longer lines than those indicating single degrees. Every 10 degrees 

 of each quadrant are numbered from to 90. 



2nd. A negative 2 inches in diameter is taken by the process 

 referred to above, and from this a transparent positive is taken on a 

 circle of micrometer glass cut to fit the tube of the microscope. It 

 is covered with a circle of thin glass cemented with balsam, and 

 mounted to fit the tube at the focal point of a positive eye-piece. 

 A cobweb is drawn across the diameter of the lower lens. When a 



