Page 627 - My FlipBook

Fig. 399. Dr. Thomas B. Hitchcock's micrometer. Description of the instninient for measurinK
the contraction or expansion of dental amalgams.
A. A steel plate witli a groove riinning from nc:ir n. at the right, to the end of the plate at the
left, and being about one inch and three-quarters long. i. i, a slot exactly one inch from the right-
hand end of the groove for the gate k to rest in while a tilling, f, is being- inserted, gg. a bar of
polished steel sliding easily in the groove, one end of which rests against the filling f. and the other
against the circular part of the pointer h. Beneath this steel plate is another, b, on which the pointer
H is suspended at c, on two points like a compass-needle, that it may move freely, j is a light spring
pressing the upi>er end of the pointer against the bar c, so that it will follow up the filling, f, in
case of contraction, e and d are slides to hold the tilling and bar down in their places, that no
upward movement might be mistaken for a contraction. This apparatus is screwed to a mahogany
board, and a paper scale arranged by means of microscope glasses, so that one degree of the scale at m
equals one thirty-six-hundredths of an inch at f.— Transactions of the New York Odontoiugical Society,
/S7-i, December meeting.