VOL. I.J PHILOSOPHICAL TRANSACTIONS. 69 



that P. Gotignies is the first that has from thence deduced the motion of Jupi- 

 ter about his axis ; and that Signior Cassini opposed it at first ; to whom the 

 said Gotignies wrote a letter of complaint on this matter. 



The same Eustachio pretends likewise, that his great glasses excel those of 

 Campani ; and that in all the trials made with them, they have performed bet- 

 ter ; and that Campani was not willing to do what was necessary for properly 

 comparing the one with the other, viz. To put equal eye-glasses in them, or 

 to exchange the same glasses. 



The said Divini affirms also, that he has found out a way to know whether 

 an object-glass be good or not, by only looking upon it, without trying. This 

 would be of good use, especially if it should extend so far as to discern the 

 goodness of such a glass, while it is yet on the cement. 



An Account of Dr. Sydenham's Booh, entitled, Methodus Curandi 

 Febres, Propriis observationibus super structa. N" 12, p. 210. 

 Dr. Sydenham's work being in the hands of every medical practitioner, it 

 would be superfluous to insert an analysis of it here ; but on this occasion it 

 may be proper to notice that the merit of this great physician and original 

 writer consist, in his accurate descriptions of what he terms epidemic consti- 

 tutions ; in his history and treatment of the small-pox ; and in his rejection 

 of the hot and cordial method of treatment in this eruptive disorder as well as 

 in fevers in general. His theoretical reasonings however are by no means 

 satisfactory ; and it has been justly observed by many medical writers, that he 

 carried one part of his cooling method of cure (viz. venesection) to too great 

 ^ a length. A short account of his life is prefixed to the English translation of 

 his works by Swan. 



Certain Problems in Navigation. By Mr. Nicholas Mercator* 



N" 13, p. 215. 



The line of artificial tangents, or the logarithmical tangent-line,-|- beginning 

 at 45 degrees, and taking every half degree for a whole one, is found to agree 



* Nicholas Mercator, an ingenious mathematician, and a learned member of the Royal Society, 

 was a native of Holstein, in Germany ; but he spent most of his time in England, where he died in 

 the year 10.90, at only 50 years of age. He was the author of many works in geometry, geography, 

 astronomy, astrology, logarithms, &c. 



t It does not appear by whom, nor by what accident, was discovered the noted property which 

 is the subject of the above memoir by Mercator, being the analogy between a scale of logarithmic 

 tangents, and Wright's protraction of the nautical meridian line, which consisted of tlie sums of the 

 secants. It appears however to have been first published, and introduced into the practice of navi- 

 gation, by Henry Bond, who mentions this property in an edition of Norwood's Epitome of Navi- 

 gation, printed about l645 5 and he again treats of it more fully in ao edition of Gunter's works. 



