VOL. IX.] PHILOSOPHICAL TRANSACTIONS. 17^ 



dional altitudes, in which 24 seconds error gives the place above one minute 

 amiss. 



At present I use tables for the sun's motion, grounded on this equation, 

 which is less than Tycho's by no less than g minutes ; which must needs cause 

 great alterations in our numbers for all the other planets ; in correcting of 

 which, I shall employ some of those minutes I can spare from my more neces- 

 sary studies, and have hopes of good success. 



Tycho's great equation made him commit no small errors, and put him upon 

 strange shifts to hide and salve them. All his observations of the planets in 

 their oppositions to the sun, are to be corrected, before we may attempt to repre- 

 sent them by numbers : for his errors in the sun's place made him err some- 

 times 5 or 6 hours in the time of the opposition, which must be reformed. 



And that I may perform my discourse of the parallax of Mars observed, I shall 

 fall upon it at my spare hours after Christmas. 



Some Observations and Experiments by Mr. Martin Lister. N** 110, p. 221. 

 I. Of the Efflorescence of certain Mineral Glebes. 



I keep by me certain large pieces of crude alum-mines, such as they were taken 

 out of the rock. I had also in the same cabinet like pieces of the ordinary 

 fire stone or marcasite of the coal-pits, which here we call brass lumps. In pro- 

 cess of time both these glebes shot forth tufts of long and slender fibres or 

 threads ; some of them half an inch long, bended and curled like hairs. In both 

 these glebes these tufts were in some measure transparent and crystalline. 

 These tufts did as often repullulate as they were struck and wiped clean off. — 

 Herein these fibres differed in taste; the aluminous very alumy and pleasantly 

 pungent; the vitriolic styptic and odious: again, the alum ones being dissolved 

 in fair water, raised a small ebullition ; whereas the vitriolic fibres dissolved 

 quietly. The alum fibres were generally smaller, and more opake, snow-like; 

 the vitriolic larger, many fibres equalling a horse-hair in thickness, and more 

 crystalline. The water wherein the alum-fibres were dissolved, gave no red 

 tincture with gall ; not by all the means I could devise to assist them ; whatever 

 has, and that with great confidence, been said to the contrary, by some of the 

 writers of our Yorkshire spaws; the vitriolic immediately gave a purple tincture 

 with gall. 



Having laid pieces of the same marcasite in a cellar, they were in a few months 

 covered over with green copperas, which was these fibres shot and again dis- 

 solved by the moist air, doddered and run together. Exposing other pieces of 

 the same vitriolic glebe in my window, where the sun came, they were covered 



A A2 



