Philosophical 'Dansactiofis. 371 



calculations respecting the magnitude of the mountain were 

 founded, and, in short, performed all those computations re- 

 corded in the Philosophical Transactions for 1778, and which 

 employed his daily labours during the greater part of two years. 

 Under these circumstances he justly complains that his name 

 has been withheld, with regard to the great share he took ia 

 those inquiries, and that assertions have been attributed to him 

 which are not justified by any thing he has written. From a 

 review of the investigations, he thinks it highly probable that 

 the mean density of the earth is five times that of water, but 

 not higher ; Mr. Cavendish has assumed the mean density 

 = 5.48, a result, upon the accuracy of which Dr. Hutton has 

 thrown much doubt. We do not think that the computations 

 founded upon the mountain experiment, derive that verifica- 

 tion from Mr. Playfair's Lithological Survey which Dr. Hutton 

 is inclined to insist upon, and we wish that he had deduced the 

 number 5. from more satisfactory data. When our author's 

 computation of the earth's density was first made, the real 

 density of the hill was unknown, " it was only known that it 

 consisted chiefly of very hard and dense rocks," much heavier 

 than common stone, which is allowed to be 2^ times the density 

 of water. 



I then, by way of example in applying the density, multiplied | by ^, 

 which produced ^ or 4| for the density of the earth, on the smallest as- 

 sumption ; till such time as we should come to know more nearly what the 

 real density of those rocks is : and therefore I must feel reason to com- 

 plain, that this number (4i) has often been stated, rather unfairly, as my 

 final conclusion for the earth's mean density ; instead of being only the 

 very lowest limit that might be used, till we could better learn something 

 on that point with more certainty. But a lithological survey of the moun- 

 tain being afterwards accurately made, at my earnest request, by that ex- 

 cellent philosopher and geologist, Mr. Play fair, the result of which was 

 published in the I'hdosnpklcal Transactions for the year IBU ; I then ap- 

 plied his mean statement of the rocks to my own calculations, which gave 

 me the number 5 for tlie density of the earth ; as I published in the four- 

 teenth volume of my edition of the PkUosophicul Transactions, and in the 

 second volume of my Tracts. 



In concluding his paper. Dr. Hutton suggests that one of the 

 pyramids in Egypt might profitably be employed instead of 

 a mountain for this experiment; such a body, he says, offers 

 several advantages ; its mass is sufficiently large, standing 

 upon a base of about the size of the whole space of Lincoln's- 

 inn Fields, and of a height almost double of that of St. Paul's 

 Steeple. 



Then the station for the plummet, or zenith sector, could be taken much 

 nearer tho centre of the mass, than on a mountain, which would give a larger 

 quantity of deviation of the plummet ; then the regular (igurc and the 

 ktiown ciiinposition of the mass would yield great facilities in the calcula- 

 tion of it* attraction ; lastly, the deviation of the pluninirt might l)e ob- 



