. The American journal of science and arts. nd surfaces of transpa-rent plates upon light.* Allerly, December 29, 1829. ** Inserted in the last number of this Journal. 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 ofminiature or pocket instruments for mathematical and philosophicalpurposes. To the pocket sextant, telescope, level, &:c. I have beendesirous to add a compass, which should have nearly the accuracy ofa surveyors large compa
. The American journal of science and arts. nd surfaces of transpa-rent plates upon light.* Allerly, December 29, 1829. ** Inserted in the last number of this Journal. 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 ofminiature or pocket instruments for mathematical and philosophicalpurposes. To the pocket sextant, telescope, level, &:c. I have beendesirous to add a compass, which should have nearly the accuracy ofa surveyors 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 satisfactionthat it has seemed to me that an account of my invention would notbe 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 mariners compass Fig. 1. This rim is made Fiff. * 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. Another has been constructed under my direction by Mr. Cox, for Mr. Bon-ney. 238 The Microscopic Compass. of brass, three inches in diameter and very light, weighing fifty the word card is inappropriate, yet as it has been coin-ed by use for that part of a compass when it moves with the needle,I shall use it in the subsequent part of this paper. Fig. 2.
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