for determining the Mean Density of the Earth, 117 



of ice have been employed for a similar purpose. The man- 

 ner likewise of putting the masses in motion was frequently 

 diversified, under the hope of being enabled thereby to obtain 

 a clue to the object of research. But the author has consi- 

 dered it needless to proceed with a detail of these fruitless 

 operations, which were carried on, without much interruption, 

 for upwards of eighteen months, and amounted in number to 

 nearly 1300 experiments. Many of these were of a mere spe- 

 culative nature, with a view to discover the cause of the ano- 

 malies here alluded to; but a thousand of them, at least, were 

 more especially made for the purpose of determining the den- 

 sity of the earth, and were eventually reduced. But the re- 

 sults, although in many cases very consistent amongst them- 

 selves, were upon the whole so discordant and unsatisfactory, 

 that no confidence could be placed on the general result, as a 

 correct value of the true object of inquiry. And, as he had 

 pre-determined not to select merely those experiments which 

 might appear to be the most favourable specimens, or sup- 

 porting any particular theory, and to keep out' of view and 

 reject the rest, he consequently abandoned the whole. 



During these investigations the author was frequently visited 

 by several scientific persons who took a lively interest in the 

 pursuit in which he was engaged, and who kindly offered him 

 their opinion and advice on several occasions. But he re- 

 marks, that he was principally indebted to Professor Forbes 

 of Edinburgh, for the most satisfactory removal of the prin- 

 cipal anomalies that he had met with. This gentleman's in- 

 timate acquaintance with the theory of heat, and its various 

 operations, effects, and influence, led him to agree with Caven- 

 dish in opinion, that one source, at least, of the anomalies 

 might arise from the radiation of heat from the masses, when 

 they were brought up to the sides of the torsion-box : and 

 that this might even still operate notwithstanding the inter- 

 position of the sides of the box, and the precautions already 

 taken. As a remedy for this influence he suggested the pro- 

 priety of having the masses gilt, and also of procuring a gilt 

 case, as a cover to the torsion-box, for the purpose of pre- 

 venting the effect of radiation, from whatever source it might 

 arise. Acting upon this advice, Mr. Baily not only caused a 

 gilt case to be made in the manner here proposed, but also 

 caused the torsion-box itself to be previously covered, all over, 

 with thick flannel. These and other alterations and improve- 

 ments having been completed, the author resolved to com- 

 mence a 7iew series of experiments, that were likely to be thus 

 made under more favourable auspices, for the correct deter- 

 mination of the mean density of the earth : and it appears 



