The Microscopic Compass. 



237 



Art. IV. — The Microscopic Compass ; invented ly John Locke, 

 M. D., Principal of Cincinnati Female Academy. 



TO THE EDITOR. 



Dear Sir — For several years I have been procuring a variety of 

 miniature or pocket instruments for mathematical and philosophical 

 purposes. To the pocket sextant, telescope, level, &:c. I have been 

 desirous to add a compass, which should have nearly the accuracy of 

 a surveyor's large compass of the best construction. 



After several fruitless attempts to procure one already made, I at- 

 tempted to invent one and have succeeded so much to my satisfaction 

 that it has seemed to me that an account of my invention would not 

 be useless or uninteresting to the public* My compass has the grad- 

 uated rim attached to the needle and revolving with it in the man- 

 ner of the card of the mariner's compass Fig. 1. This rim is made 



Fiff. 1. 



* I commenced my experiments on this instrument in Feb. 1832. I presently- 

 had one constructed for myself by a very ingenious young artisan of this city Mr. T. 

 Wells. Another has been constructed under my direction by Mr. Cox, for Mr. Bon- 

 ney. 



