408 Life of the Rev. John Flamsteed, [Dec. 



elliptical or hyperbolical glasses all the rays of light that 

 fall on the object parallel to the axes may be collected into 

 one point of the image in the distinct base, supposing all 

 the rays of light of the same species and liable to the same 

 law of refraction ; which yet Mr. Newton demonstrated 

 they were not, by many experiments published in this year's 

 Transactions : and this is the only thing that I can perceive 

 for which Descartes' Dioptrics have been so celebrated. I 

 finished my transcript of Mr. Gascoigne's papers May 12th, 

 176*2. The spare hours of the remaining part of the year 

 were employed in my observations, as the weather suffered 

 me; in preparing advertisements of the Appulses of the 

 moon and planets to fixed stars for the following year; 

 which were printed by Mr. Oldenburg in his Transactions, 

 with some observations of the planets I imparted to him. 



Whilst I was enquiring for the planets' appulses to the 

 fixed stars by the help of Hecker's ephemerides, I found 

 that in September, 1672, the planet Mars, then newly past 

 his perihelion and opposition to the sun, would pass amongst 

 three contiguous fixed stars in the water of Aquarius : and 

 that, by reason he was then very near the earth, this would 

 be the most convenient opportunity, that would be afforded 

 of many years, for determining his, and consequently the 

 sun's horizontal parallax. I drew up a monitum of this 

 appearance, and sent it with a letter to Mr. Oldenburg, 

 who printed it in his Transactions, No. 86, August 19th, 

 1672: having before sent my admonition into France, where 

 the gentlemen of their Accademy took care to have it ob- 

 served in several places. My father's affairs caused me to 

 take a journey into Lancashire, the very day I had designed 

 to begin my observations : but God's Providence so ordered 

 it that they gave me an opportunity to visit Townley, where 

 I was kindly received and entertained by Mr. Townley, with 

 whose instruments I saw Mars near the middlemost of the 

 three adjacent fixed stars. My stay in Lancashire was short : 

 at my return from thence, I took his distances from two of 

 them at distant times of the night. Whence I determined 

 his parallax then 25 ", equal to his visible diameter ; which 

 therefore must be its constant measure; and consequently 

 the sun's horizontal parallax not more than 10". This I 

 gave notice of in the Transactions, No. 96 : and the French, 



