636 MISCELLANEOUS PAPERS. 



tained by weighing, so that the determination of the density of the 

 earth enters into the realm of laboratory investigation. However, this 

 sensitiveness which eliminates the uncertainty in the computation of 

 the attracting forces has, as a consequence, some disadvantages which 

 were first mentioned by Francis Baily while engaged ui^on the same 

 problem. These drawbacks consist chietly of a limited inertia and sta- 

 bility against accidental disturbances, especially temperature changes 

 and the variations in the twisting force of the supporting thread. In 

 the interesting investigations of A. Cornu and J. B. Bailie the disturb, 

 ances just referred to seem to have been essentially eliminated. Unfor- 

 tunately it is not possible to form an opinion regarding the accuracy of 

 the results from the short report that is given in Compt. Eend., 1878, 

 Lxxxvi, pp. 699-702. At all events measurements with the torsion 

 balance must be regarded as especially difficult. 



For this reason the fourth method, the determination by the means of 

 a balance of the change in weight of a body caused by the proximity of 

 a second body of known mass, has the preference. It is true, however, 

 that the ordinary balance is not sufficiently sensitive to measure the 

 attraction of bodies as small as those employed in the torsion balance. 

 Jolly, who lirst made use ot this method, utilized a ball of lead of 120 

 hundredweight. At this time Messrs. Kiinig and Richarz are working 

 at Jolly's method, using a parallelepiped block of lead of 2,000 hun- 

 dredweight. Since it is necessary to actually determine the weight of 

 these large bodies, a task rendered difficult on account of their size, 

 the measurement of their attraction requires the transposition of them 

 while being weighed. Jolly had four scale ijans, two of which were 

 fastened below the others by a wire 2L meters long; he determined the 

 increase in the weight of a glass vessel filled with mercury which was 

 caused by its transfer to the lower scale pan under which was the at- 

 tracting ball of lead. This transfer caused a loss of time, and necessi- 

 tated a frequent stoppage of the balance, a condition which might seri- 

 ously affect the results since the change in the relative positions of 

 knife edge and its resting place would bring about a deformity in the 

 former, causing a disturbance in the oscillation of the balance. 



I have' sought to overcome these difficulties by turning the instru- 

 ment through dO^, that is, by replacing for a horizontal balance a verti- 

 cal one or a pendulum whose knife-edge is above the center of gravity 

 and very near to it, upon the hypothesis that the sensitiveness of the 

 apparatus could be materially increased if it forms a rigid system and 

 is protected from flexure by being supported with its length vertical. 

 Then it is ])ossible to succeed with smaller and more easily handled 

 masses, and to prosecute the observations without difficulty while the 

 necessity to stop the insti ument during the progress of the work is en- 

 tirely avoided. A trial apparatus was constructed in which the time of 

 oscillation was prolonged to the desired extent, giving results so har- 

 monious that a final pendulum was completed in 1885 by Kepsold, 



