114 RBPOET— 1881. 



He seems to have failed to detect the laws governing the longer and 

 wider oscillations performed. Notwithstanding that he took a number of 

 precautions against the effects of changes of temperature, he remarks 

 that 'the external circumstances under which the above experiments 

 were carried out must be characterised as extremely unfavourable for this 

 object (measuring the lunar attraction), so that the sensitiveness might be 

 much increased in pits in the ground, provided the reaction of the glowing 

 molten interior against the solid crust do not generate inequalities of the 

 same order.' 



Further on he says that if the displacements of the pendulum should 

 be found not to agree in phase with the theoretical phase as given by the 

 sun's position, then it might be concluded that gravitation must take a 

 finite time to come from the sun. 



It appears to me that such a result would afford strong grounds for 

 presuming the existence of frictional tides in the solid earth, and that 

 Professor Zollner's conclusion would be quite unjustifiable. 



Earlier in the paper he states that he preferred to construct his instru- 

 ment on a large scale, in order to avoid the disturbing effects of convection 

 currents. We cannot but think, from our own experience, that by this 

 course Professor Zollner lost more than he gained, for the larger the 

 instrument the more it would necessarily be exposed in its various parts 

 to regions of different temperature, and we have found that the warping 

 of supports by inequalities of temperatui'e is a most serious cause of 

 disturbance. 



The instrument of which we have given a short account appears to us 

 very interesting from its ingenuity, and the account of the attempts to 

 use it are well worthy of attention, but we cannot think that it can ever 

 be made to give such good results as those which may perhaps be attained 

 by our plan or by others. The variation in the torsional elasticity of the 

 suspending springs, due to changes of temperature, would seem likely to 

 produce serious variations in the value of the displacements of the pendu- 

 lum, and it does not seem easy to suspend such an instrument in fluid in 

 such a manner as to kill out the effects of purely local tremors. 



Moreover, the whole instrument is kept permanently in a condition of 

 great stress, and one would be inclined to suppose that the vertical stand 

 would be slightly warped by the variation of direction in which the 

 tensions of the springs are applied, when the pendulum bob varies its 

 position. 



In a further paper in the same volume, p. 140, ' Zur Geschichte 

 des Horizontalpendels,' Zollner gives the priority of invention to M. 

 Perrot, who had described a similar instrument on March 31, 1862, 

 (' Comptes Rendus,' vol. 54, p. 728), but as far as he knows M. Perrot 

 did not actually construct it. 



He also quotes an account of an ' Astronomische Pendelwage,' by 

 Lorenz Hengler, published in 1832, in vol. 43 of ' Dingler's Polytechn. 

 Journ.,' pp. 81-92. In this paper it appears that Hengler gives the 

 most astonishing and vague accounts of the manner in which he detected 

 the lunar attraction with a horizontal pendulum, the points of support 

 being the ceiling and floor of a room 16 feet high. The terrestrial rotation 

 was also detected with a still more marvellous instrument. 



Zollner obviously discredits these experiments, but hesitates to 

 characterise them, as ihey deserve, as mere fraud and invention. 



The university authorities at Munich state that in the years 1830-1 



