MiJceUanea Curiofa. 3 1 5 



A Letter of "Dr. Wallis to T>r. 

 Sloane r concerning the Generation 

 of liail^ and of "Thunder and 

 Lightning^and the Ejfefis thereof 



Oxon. "July 26. 1697. 



S I 



I Thank you for the Tranfa&ions of June 

 X which you fent me ^ wherein I am' well 

 pleafed with Mr. Halky\ Remarks on the 

 Torricellian Expeiiment at the top of Snow- 

 don-hill in Wales^ at the height of 1240 yards 

 perpendicular. Where the, height of that 

 Quickfilver in the Barofcope was 3 Inches 

 and fo lefs than below at the Sea-fide;, \ which 

 is an Obfervation of good ufe , and would 

 have been more fo, had he had the leifure to 

 make like Obfervations at feveral other per- 

 pendicular heights in the Afcent. For 

 from fuch comparative Obfervations we are 

 to make an Eftimate, at what proportion the 

 height of the Qpickfilver doth decreafe in re- 

 ference to the height of the place. I mean 

 whether in the fame Proportion, or the Du- 

 plicate , Sub-duplicate , or how otherwife 

 Complicate thereof. From whence we may 

 make a Judgment of the height of the Atmos- 

 phere , if at leaft it have a determinate 

 height. I did once attempt (a great while 

 fince) a Computation of it ^ but wanted a 

 fufficient number of D&ta to proceed upon. 



