Lesley.] -0~t [April 18, 



acquaintances, but remained a solitary specimen until Mr. Kerr, State 

 Geologist of North Carolina, begged permission to have it copied at Mr. 

 Young's (Jr.) establishment. This was in the winter of 1871, '72. I have 

 since been informed*by Mr. Kerr that his order was never filled ; at least* 

 he never received his Micrometer. The original was in constant use by 

 one of my assistants in my office throughout the spring and summer of 

 1872. When the course of instruction in the new Department of Science 

 of the University of Pennsylvania commenced last fall I accustomed my 

 special geological students to use this instrument among others, and 

 ordered of Heller & Brightly, instrument-makers, a duplicate of it, set 

 however not to centimeters and millimeters, but to inches and hundreths 

 of an inch. While making it, Mr. Eckley Coxe and other civil and 

 mining engineers saw it, and ordered others like it for their own use, 

 and these orders have become so numerous that it has evidently taken 

 its place among the accepted apparatus of the engineer's office-table. I 

 hope many will in future enjoy the relief and comfort from it which I 

 have enjoyed since 1868. 



I was urged to patent it, as Mr. Cleaver patented his Protractor. But 

 I feel a natural prejudice against patenting a little thing which may be- 

 come to some extent a public benefit, at all events within the not alto- 

 gether narrow limits of one of the scientific professions. I desire, 

 however, to prevent any one else from hampering its progress by a 

 patent, and to that end beg leave to place this record of its invention 

 among the Proceedings of this Society. Any one can obtain the instru- 

 ment free of patent royalty, from the makers above named, or may 

 order it made for themselues anywhere else. 



This Micrometer consists of an arc set with three, four or more needle- 

 points fixed at intervals of one centimeter, one-half inch, or any other 

 unit adopted for the survey, equivalent say to 100 feet (yards, links, 

 rods, &c). 



A handle projects upward from the inside of the arc by which to hold 

 it, and by which it may be applied to the line of course and be gently 

 rotated, so that each needle-point in its turn pricks its (100 feet) unit 

 distance along the line. 



Between the last two needle-points floats a supernumerary needle- 

 point or compass-leg, jointed high up on the handle, and swung or 

 floated to and fro by a simple ratchet and watch chain, turned at will by 

 means of a button, projecting from the centre of a circular disc on the 

 handle ; the disc circle being divided into hundredths (thousandths, 

 &c.,) and traversed by an index which starts from and comes round to 

 a stop at zero. 



While the index travels over the disc from to 100 the supernumerary 

 needle-point travels from needle-point to needle-point, one unit. 



Example of use : Suppose a distance 327 feet to be laid off on a 

 course ; the fifth needle is applied to the station (point of tangent, or 

 point of curve) and the arc rotated, so that the fourth needle pricks 100, 



