April 18, 1873.] ~do [Lesley. 



DESCRIPTION OF LESLEY'S MICROMETER FOR FIELD-NOTE 



PLOTTING. 



(Read before the American Philosophical Society, April 18, 1873.) 



I desire to place on record in the Proceedings of the Society a de- 

 scription of my Micrometer for plotting field-notes, which appears to be 

 coming into favor with Civil and Mining Engineers. 



It was many years ago that the need of such a little instrument forced 

 itself on my attention, as a substitute for a vernier attachment to a scale 

 for use on the office-table. The strain upon the eyes in constant plotting 

 on small scales, say on the common scale of 1000 feet to the inch, or the 

 not uncommon one of 2000, is greater than the best human organs of 

 vision can endure without permanent injury ; to say nothing of the loss 

 of time involved in adjusting the dividers, or applying the paper edge, 

 if a paper scale be used directly. Every field worker who has con- 

 structed elaborate contour line maps covering an extensive region of 

 country will bear me out in this assertion. 



Considering also the liability to error in counting the decimals and 

 hundredths or thousandths of the scale-unit of distances, after hours of 

 application to work has lowered the tone of the nervous system, I sought 

 some mechanical substitute analogous to Mr. Cleaver's Protractor, now 

 in almost universal use for plotting courses with ease and precision. 



Many forms of such an instrument passed through my mind ; but over 

 occupation, or perhaps laziness, prevented me from taking the necessary 

 steps to realize the idea in even tentative forms, although I spoke of it 

 several times to Mr. Young, the accomplished and experienced instru- 

 ment-maker of Philadelphia, now dead. 



During my wanderings in Europe in search of health in 1866, '67 and 

 '68, I was several times the guest of my old friend and fellow-laborer in 

 the Anthracite coalfields (1853), Prof. Edouard Desor, at his charming 

 residences on the Combe Varin and in Neufchatel, Switzerland. One 

 day we strolled into the well-known philosophical instrument manufac- 

 tory of Mr. Hipp, to whom, among other things, I mentioned the need of a 

 Micrometer Divider for plotting, and drew at his request three of its 

 possible forms, such as seemed to me the most feasible, giving him an 

 order for one, and leaving him to select the form he preferred. 



On my return to Philadelphia in the spring of 1868 I received it in a 

 broken condition. The chain had been snapped by some custom-house 

 official, too curious to learn its nature to treat it with much delicacy of 

 handling. It was however easily repaired, and I found it all I could de- 

 sire : handy, accurate in its action, and perfectly relieving the eyes from 

 the strain of measuring. It was much admired by my professional 

 a. p. s. — vol. xiii. 2d 



