PROFESSOR RIGAUD, ON THE RELATIVE QUANTITIES 



A 



the immediate operation requires, all is gained that can be hoped for. 

 The results, which are now about to be described, were all obtained 

 during the summer in this manner: each piece was weighed before 

 the land was cut from the water, the separate parts were then 

 weighed independently; this was usually repeated,' when the second 

 was very seldom found to vary from the first determination by tV of 

 a grain, and the sum of the parts most commonly made up exactly 

 the weight which had at first been found to belong to the whole. 



Dr Halley points out another difficulty, for lie says "that the map 

 consisting of several sheets of paper, they were found to be of dif- 

 ferent thickness or compactness, so as to make a sensible difference, 

 which obliged me to examine the proportion between the weight and 

 acre in each sheet." Dr Long refers to this where he observes that 

 "the paper whereon it" [the engraving of the globe] "is printed 

 should be of an equable thickness as near as possible." JNlr Addison 

 obligingly endeavoured to obviate any such cause of inaccuracy by 

 taking care that the impressions should be worked off on paper of an 

 uniform texture. It was not possible to succeed in this so far as to 

 have all the equal gores of the same weight, but there were hardly 

 any knots to produce partial inequalities, and, by working out the 

 results separately for each part, as near an approximation to the truth 

 was upon the whole arrived at as the method seemed capable of pro- 

 ducing. Relative quantities are all that were required, and by this 

 means they rested on the uniformity of paper only of a small com- 

 parative size, a quality which might be assumed witliout any material 

 error. The plates of Mr Addison's globe cover a plane surface of 

 4071^ square inches, and from the many parts, into which they are 

 of necessity divided, there is a fair chance for compensation, because 

 it may be presumed that if the land were on the thicker part in one 

 instance, it might be on the thinner in another. This compensation, 

 being a general effect, might at first sight appear to be best secured 

 by weighing all the land of the globe together, and all the water; 

 but in addition to other advantages in the different process, there are 

 objections to this method, which make it inexpedient. It would require 

 constant and long attention in keeping the respective parts together 



