574 SCIENTIFIC RECORD FOR 1883. 



scales. To the screw of bis slide rest, the pitch of which was one-eighth 

 of an inch, a micrometer head was attached having two rows of holes, 

 one of 25 and the other of 127. On the former row, 20 holes correspond 

 obviously to one-tenth of an inch, 4 to one fiftieth, aud 2 to one hun- 

 dredth. On the latter, 40 holes give one millimeter, 4 holes one-tenth 

 of a millimeter, &c. (Phil. Mag., March, 1883, V, xv, 217.) 



Extended descriptions have beeu published of the buildings and ap- 

 paratus of the International Bureau of Weights and Measures, now 

 located in the Park of St. Cloud, near Paris. This bureau was origi- 

 nated in 1875, and had for its object the securing of an accurate interna- 

 tional metric system. Sixteen countries are represented in it and con- 

 tributed a million francs toward its expenses. The apparatus employed 

 is the most perfect attainable, and the measurements are made with the 

 greatest possible accuracy. (Nature, September, 1883, xxvin, 464, 592.) 



The foot-measure in China varies largely with different trades and in 

 different parts of the country. The carpenter's rule at Ningpo has a 

 foot of less than 10 inches, while that of the junk-builders at Shang- 

 hai has a foot of nearly 16 inches. The standard foot of the Pekin Im- 

 perial Board of Works is 12£ inches. A copper foot-measure of the year 

 A. D. 81 is 9£ inches. (Nature, June, 1883, xxvin, 207.) 



Tresca has communicated to the French Academy the results of his 

 examination of two platinum meters which originally belonged to Prony 

 and were used by him in the early part of the century, in connection 

 with the labors of the first metric commission. Both are end meters, 

 but one of them is also a line meter. One of the end meters is 13.98 

 microns shorter than the meter of the archives ; the other end meter 

 is 7.94 microns shorter, while the line meter upon the latter is 30.55 mi- 

 crons shorter. (C. E., March, 1883, xcvi, 667.) 



Terquem has described an improved cathetometer constructed for 

 him by Dumoulin-Froment. Among other modifications, this instru- 

 ment has only a single slide, the telescope being carried on a plate mov- 

 ing on the face of this slide by means of a micrometer screw. This very 

 considerable improvement was used in cathetometers constructed by 

 William Gruuow, of New York, ten or twelve years ago. The reading- 

 is to 0.01 millimeter. (J. Phys., November, 1883, II, n, 496.) 



Rayleigh has suggested the use of an electro-magnetic damping appa- 

 ratus to control the oscillations of a balance. Two magnets of steel 

 wire 3 or 4 inches long are attached vertically to the scale-pans and 

 underneath one of them is fixed a coil of insulated wire of, perhaps, 

 fifty or one hundred turns and 4 or 5 inches in diameter, placed imme- 

 diately under the balance case. On completing the circuit of a Le- 

 c'anche cell through the coil by means of a key, at suitable intervals, 

 the beam may be brought to rest very promptly. He has also sug- 

 gested quicker vibrating beams, the delicacy being restored by magni- 

 fying the displacement by means of a lens, the scale being illuminated 

 if necessary. (Nature, November, 1883, xxix, 91.) 



