204 THE MICROSCOPICAL NEWS. 
MICROMETRY. 
T the meeting at Chicago of the American Society of Micros- 
copists last year, the ‘“‘ National Committee on Micrometry” 
presented a report of their proceedings, a reprint of which has now 
reached us. We learn from this report that*at the Session in 
Indianapolis in 1878, the Society adopted a resolution referring to 
the various Microscopical Societies certain questions pertaining to 
Micrometry. Dr. R. H. Ward, who was then President of the 
Society and also of the Troy Scientific Association, addressed a 
communication to all the Societies interested, in consequence of 
which there was formed a Committee, which ultimately included 
Prof. W. Ashburner, of the San Francisco Microscopical Society ; 
Prof. F. A. P. Barnard, American Metrological Society ; Dr. Lester 
Curtis, Illinois Microscopical Society; Dr. G. E. Fell, Buffalo 
Microscopical Society ; Dr. Henry Jameson, Indiana Microscopical 
Society ; Prof. S. A. Lattimore, Rochester Academy of Sciences ; 
_ Rey. S. Lockwood, New Jersey Microscopical Society ; Prof. E. W. 
Morley, American Association for Advancement of Science; Dr. 
G. Richardson, American Postal Microscopical Society ; Prof. W. 
A. Rogers, Harvard University; Prof. S. P. Sharpless, Boston 
Microscopical Society ; Prof. H. L. Smith, Hobart College, Geneva, 
N. Y.; Prof. A. H. Tuttle, Microscopical Society, Columbus ; C. 
M. Vorce, Cleveland Microscopical Society ; and Dr. J. J. Wood- 
word, U.S. Medical Museum, Washington. 
For the unit in Micrometry, the Committee adopted the mzcron 
(u% =r900 “m.), and for their standard a centimetre scale obtained 
for them by Prof. Hilgard, the Superintendent of the U. S. Coast 
Survey. This scale was verified “ with great care” by Prof. C. S. 
Peirce in 1882, and again last year by Prof. W. A. Rogers. The 
scale was examined with a half-inch objective supplied with a 
Tolles’ opaque illuminator, and the defining lines were found to be 
of the most beautiful character. The scale is marked on a plate 
made of platinum and iridium (10 °/, iridium), and is divided 
into ten millimetres, one of the millimetres being divided into 
tenths, and one of the tenths into spaces of ten microns. The 
accuracy of the scale was determined by comparison with a 
standard which, it is stated, had been verified by Prof. Tresca at 
Paris, and Mr. Chaney, the warden of the standards at London. 
It was resolved by the committee that this scale, ‘Standard 
Micrometer, Centimetre A, 1882,” should not pass out of the hands 
of the Treasurer of the Society, except to persons of eminent 
ability. 
In connection with this subject, we may also refer to a paper 
recently written by Prof. W. A. Rogers on “A critical study of the 
