0it ' Experiments to detertitiiie tfie Denfit^ of the Earth 



I copy Mr. Cavendifh's concluding remarks in his own words : 



" From this table it appears, that though the experiments agree pretty Well together, 

 f^t the difference between them both in the quantity of motion of the arm and In the time 

 di vibration is greater than can proceed merely from the error of obfervation. As 

 to the difference in the motion of the arm, it may very well be accounted for from the cur- 

 rent of air produced by the difference of temperature ; but whether this can account for 

 the difference in the time of vibration is doubtful. If the current of air vns regular, and of 

 the fame fwiftnefs in all parts of the vibration of the ball, I think it could not -, but as there 

 will mod likely be much irregularity in the current, it may very likely be fuflicient to ac- 

 count for the difference. 



" By a mean of the experiments made with the wire firfl. ufed, the denfity of the earth 

 comes out 5,48 times greater than that of water; and.by a mean of thofe made with the 

 latter wire it comes out the fame ; and the extreme difference of the refults of the twenty- 

 three obfervations made with this wire is only ,75 ; fo that the extreme refults do not dif- 

 fer from the mean by more than ,38, or -^-th of the whole, apd therefore the denfity fhould 

 feem to be determined hereby to great exadlnefs. It indeed may be obje£led, that as the 

 refult appears to be influenced by the current of air or fomc other caufe, the laws of which 

 we are not well acquainted with, this caufe may perhaps aft always or commonly in the 

 Came direftion, and thereby make a confiderable error in the refult. But yet, as the ex- 

 periments were tried in various weathers and with confiderable variety in the difference of 

 temperature of the weights and air, and with the arm refting at different diftances from the 

 Cdes of the cafe, it feenis very unlikely that this caufe fkould adt fo uniformly in the fam» 

 ^ay as to make the error of the mean refult nearly equal to the difference between this 

 tnd the extreme ; and therefore it feems very unlikely that the denfity of the earth {hould 

 differ from 5,48 by fo much as -jVth of the whole. 



" Another obje£tion perhaps may be made to thefe experiments, namely, that it is uncer- 

 tain whether in thefe fmall diftances the force of gravity follows exadtly the fame law as in 

 greater diftances. There is no reafon however to think that any irregularity of this kind 

 takes place until the bodies come within the aftion of what is called the attra£lion of co- 

 hefion, and which fecms to extend only to very minute diftances. With a view to fee 

 whether the rcfuit could be affedled by this attradlion, I made the 9th, 10th, nth, and 15th 

 experiments, in which the balls were made to reft as clofe to the fides of the cafe as they 

 could j but there is no difference to be depended on between the refults under that circum- 

 ftance and when the balls are placed in any other part of the cafe. 



" According to the experiments made by Dr. Mafkelyne on the attraftion of the hill 

 Schehallien, the denfity of the earth is 4'- times that of water; which differs rather more 

 from the preceding determination than I fhould have expected. But I forbear entering into 

 any confideration of which determination is moft to be depended on, till I have examined 

 more carefully how much the preceding determination is affected by irregularities whof« 

 j^uantity I cannot meafure." 



VJ. An 



