VOL. LVI.] PHILOSOPHICAL TRANSACTIONS. 291 



XV. Specimen of some New Electrical Experiments. By John Baptist 



Beccaria* F. R. S. p. 105. 

 These experiments may be consulted to more advantage in the author's 

 published works on electricity, which are very curious and valuable. 



XVI. Proposal of a Method for Measuring Degrees of Longitude on Parallels 

 of the Equator. By J. Michell, B.D., F. R. S. p. IIQ. 



There have been already several attempts made towards discovering the figure 

 of the earth, by measuring the length of a degree of the meridian in different 

 latitudes : now if these measures had been sufficiently accurate and numerous, 

 and we could also depend on the uniformity of the earth's surface, we might then 

 immediately discover from them the form sought; but these measures, not 

 agreeing exactly to any certain rule, leave us still in some degree at a loss. It 

 is therefore much to be wished, that more measurements of degrees on the me- 

 ridian were to be made, in order to determine with greater accuracy a question of 

 this importance. But what would tend yet more to determine this matter, 

 would be the measurement of degrees of longitude as well as those of latitude. 

 Astronomers have indeed expressed their wishes that this might be done, and 

 though no attempt has been hitherto made towards it, yet as it is probable, that 

 such measurements may some time or other take place, it will not be amiss to 

 suggest a method, which will admit of more exactness than any I have seen 

 proposed for this purpose, all of which, depending on an observation of the 

 time, are therefore liable to an error of 15 seconds of a degree for every second 

 of time ; but the method Mr. M. recommends, stands on the same foundation 

 with the measurement of a degree of the meridian, and, the instruments being 

 equally good, and the number of miles to be measured the same, the exactness 

 of it, to that of a degree of the meridian, will be in the proportion of the sine 

 of the latitude to the radius very nearly. 



In pi. 5, fig. 1 1, let AB represent the equator; p the pole; dlep a parallel of 

 the equator ; pec a meridian passing through the station e ; plmn a meridian 

 passing through another station m ; and let ameb be a great circle cutting the 

 meridian pec at right angles in the point e. 



Then in the spherical triangle amn, right angled at n, we shall have r : cos. 



♦ J. B. Beccaria was successively professor of philosophy at Palermo, Rome, and Turin, where 

 he was in great favour with the King of Sardinia, and became tutor to his sons. He was an 

 ingenious philosopher, and published some valuable works, particularly on electricity, in which he 

 was more remarkably distinguished. He published also an account of his measurement of a degree 

 of the meridian near Turin, which he carefully executed between the years 176'0 and 176^. 

 Mr. B. was a native of Mondovi in Piedmont; and he died in 1781; but at what age does not 

 appear. 



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