332 RECORD OF SCIENCE FOR 1886. 



Wolf has presented a paper to the Freucli Academy on the autlientic- 

 ity and exact value of the Peruvian unit of length preserved in the 

 Paris Observatory. Since the French legal meter is defined as a 

 determined fraction of this standard unit taken at the temperature 

 of 13° Eeaumur, the importance of ascertainiug its exact value and its 

 state of preservation is obvious. Moreover, as the same standard was 

 used for the measurement of an arc of the meridian in Peru, it forms 

 the connecting link between the older and the more recent geodetic 

 operations. For these reasons, this meter has become an object of the 

 highest interest, not only for France but also for the whole scientific 

 world. The author replies in detail to the doubts and objections raised 

 by Peters and others in Germany against its authenticity and state of 

 preservation ; and at his request a committee was appointed by the 

 academy consisting of Faye, Monchez, Janssen, F. Perrier and Wolf, to 

 consider the whole question. (Nature, March, 1886, xxxiii, 503). 



A paper on the normal meter has been presented to the Berlin Phys- 

 ical Society by Pernet. After a brief historical introduction, the paper 

 discusses the events which in 1878 led to a new international agreement, 

 in consequence of which a new normal meter of platinum-iridium of x 

 form was prepared and compared, with the meter of the archives. The 

 paper describes minutely the arrangements of the Bureau in which the 

 comparisons were undertaken, the .contrivances for securing the sev- 

 eral comparing rooms against outward disturbances, the means adopted 

 for insuring constant temperatures, and the methods employed in .the 

 comparisons as also in the deJ;ermination8 of the expansion-coefficients 

 of the rods used. His own especial labors had for their object the com- 

 parison of a series of normal meter rods of different metals with the 

 meter of the archives and the determination whether repeated heatings 

 and coolings between 50° and 0° C, whether concussions, and whether 

 time caused any perceptible changes in the lengths of the rods. As the 

 result of these investigations it was found (1) that the compared national 

 standards, together with their divisions, were exact up to one-thou- 

 sandth of a millimeter; (2) that, with the exception of steel (which on 

 account of its changes m hardness, readily yielded modifications of 

 volume and length in the rods made of this material), all the metals out 

 of which the standards were made — namely, platinum-iridium, i)latinum 

 and brass — furnished material suitable for normal meter rods 5 and (3) 

 that repeated heatings and concussions induced no changes passing be- 

 yond the limits witiiin which observation fails. (Nature, May, 1886, 

 XXXIV, 22.) 



The ninth report of the Comite International des Poids et Mesures has 

 been issued. During the year 1885, new instruments have been obtained 

 at a cost of about $2,500, for the accurate comparison of standards of the 

 metric system. These include a comparator for length measurements 

 made by Brunner; mercurial thermometers, by Tounelot; an air ther- 

 mometer, by Golaz ; a spheroraeter, by Brunner, and other measuring 



