VOL. XL.} PHILOSOPHICAL TRANSACTIONS. 12S 



found it necessary to have a more exact knowledge of the magnitude of each 

 degree, not only in great measures, as in miles and leagues, but also in perches, 

 toises and feet. 



As to Russia, the geographical measures of which are wersts, divided each 

 into 500 sagenes, and each sagene supposed to be exactly 7 feet English ; this 

 proportion once known, and the exact ratio of the English to the French foot, 

 or to the toise of 6 feet, which the French astronomers employed in their 

 measurements, and of which they found a degree of a great circle contained 

 57060 ; if it be asked what more is requisite for concluding that a degree of a 

 great circle contains 104-1- wersts ? and what remains towards the perfection of 

 the geography of Russia, in the most minute detail, but to employ this mea- 

 sure of wersts, sagenes, and English feet, in actual measurements; and to con- 

 struct the charts by the most exact methods of geometry ; it may be answered, 

 we should be very happy, if in the geography of Russia we were arrived at this 

 pitch ; not only in the general map, but in that of any particular district, the 

 nearest and of most concern to us. But besides that we are as yet far from pre- 

 tending to this ; it may be made to appear, that it is not possible to attain it, 

 without undertaking an equal, and even a greater work than all that has been 

 hitherto done in France and elsewhere, towards the measurement of the 

 earth. 



For if the earth be not truly spherical, all the degrees of the great circles will 

 not be equal to each other ; and those of the small circles, taken at a certain 

 distance from their parallel great circles, will not have the same relation that 

 the degrees of the smill circles, taken at the same distance, would have on a 

 sphere. In all this there might possibly arise an infinite variety, according to 

 the figure the earth might have; and as it is not yet decided what is the earth's 

 true figure, and that there is no better method of ascertaining it than by obser- 

 vations made in so great an extent as that of Russia; therefore the perfection' 

 (of the geography of Russia stands in need of this great undertaking ; which, 

 besides its usefulness, will yield much honour, by contributing towards the de- 

 ciding the celebrated question of the earth's figure. 



There have been some who have long since suspected, and even thought 

 they were furnished with proofs, that the earth is not exactly spherical. But 

 supposing the earth to be bounded by a curve surface, such as it would be by 

 the level of the sea carried quite over all the earth; it is in this manner, the 

 earth being considered as covered with a fluid, that Sir Isaac j^ewton, in the 

 first edition of his Principia, has demonstrated, that supposing this fluid homo- 

 geneous, and the earth to have been at rest at the time of its creation, it must 

 have assumed the figure of a perfect sphere: but afterwards, supposing it to 



