238 PHYSICS. 



of passing a wire through ice without cutting it in two, divides plastic 

 substances into two classes. Those belonging to the first class, (ian, like 

 ice, be cut in two with a metallic wire, and can be considerably deformed. 

 To this class belong plastic clay, fresh soap, camphor, black pitch. Sub- 

 stances classed in the second group give two lamellse on the two sides 

 of the cutting wire, which then come out of the slit, become notched and 

 bend over, resembling leaves. Examples of this class are found in veg- 

 etable Japanese wax, dry Marseilles soap, tallow, and stearin, and 

 especially yellow wax and paraffin. The success of the experiment de- 

 pends on the size of the wire and on the temperature. For yellow wax, 

 the wire should be from ^ to 1™™, diameter ; for paraffin ^ to 0.9. The 

 leaves with the former are produced between — 8° and 40°, with the lat- 

 ter (melting at 43o.5) only up to 15°. The author calls attention to the 

 similarity between these lamellae and those separated from a rail when 

 a locomotive goes down a steep incline rapidly and with a powerful 

 brake applied. — {Wature, xxi, 21, 1879.) 



Herschel has published a paper on the use of the seconds pendulum 

 for determining the figure of the earth, in which he comes to the conclu- 

 sion that the experiments made hitherto are of little use, since the prob- 

 lem to be solved was so imj)erfectly grasped. The use of the absolute 

 pendulum contemplated two distinct objects which had no essential con- 

 nection, the force of gravity and the figure of the earth ; while the use 

 of the differential pendulum contemplated only one. The rate of the 

 seconds pendulum varies along the actual equator, and the value of grav- 

 ity at the equator is therefore only an idea. — {Nature, xxi, 599, 1880.) 

 O. S. Peirce has given the results of his pendulum experiments made 

 under the direction of the Coast Survey. The values obtained were : 

 At Hoboken, 0.9932052°' ; at Paris, 0.9939337 ; at Berlin, 0.9942399 ; at 

 Kew 0.99417 7G. Eeduced to the sea-level these numbers become 0.993- 

 2074, 0.9939500„0.9942482, and 0.9941790. Eeduced to the equator, they 

 are : 0.9910003, 0.9910132, 0.9909865, and 0.9910083. These values, the 

 author thinks, will have to be diminished by about 20 microns on ac- 

 count of the error of the standard of length emx^loyed.— (Aw. J. Sci., 

 Ill ,xx, 327, October, 1880.) Mendenhall has made a series of experi- 

 ments to determine the force of gravity at Tokio, Japan. In the earlier 

 part of the investigation a Kater pendulum was used ; in the latter, one 

 of Borda's construction. The beats were recorded upon a chronograph 

 at the same time with those of a break-circuit clock, the length of one 

 second upon the sheet being about 8™"", so that it could easily be 

 subdivided. Since it was only the fractional part of a second by which 

 the two pendulums differed, that was to be determined, the standard 

 pendulum was only required to break the circuit twice, once at the be- 

 ginning and again at the end of the experiment. Asa mean of six ex- 

 periments with the Kater pendulum the value of "</" was found to be 

 9.7974 ; the mean of eleven experiments with the Borda pendulum gave 

 9.7984.— (Am. J. Sci., Ill, xx, 124, August, 1880.) 



