140 



PHILOSOPHICAL TRANSACTIONS. 



[anno 1771. 



Mens, de Luc, of Geneva, has given a method to measure the different ele- 

 vation of places by barometers, founded on his own observations, far more exact 

 than any other before him : his rule is, ' the difference of the logarithms of the 

 height of the quicksilver, in the two places, reduced into French lines, and the 

 logarithms carried to 5 places, including the characteristics, will give the difference 

 of elevation in tpises, if Fahrenheit's thermometer be nearly at 66" ; but about 

 -rV must be deducted from the elevation so given, if the thermometer be at 55° or 

 temperate.' 



29.993 English inches = 337-824 French lines, log, 25286.8 

 29.752 ditto =335.110 ditto log. 25251.9 



difference .... 34.9 toises, or 

 209.4 French feet = 223 English feet nearly ; from which if iV = 12^ nearly be 

 deducted, 2104- feet remain for the difference of elevation of Mr. P.'s room and 

 the surface of the sea ; which differs 6-^ feet from the result given by the first 

 hypothesis. 



The greatest height observed, in these 5 years, with a good Fahrenheit's ther- > 

 mometer, screened from the sun in a s. w. room, was as follows at noon : 



1765 August 23d 1 



1766 August 9th 1 7 go 

 1769 July 7th J 



the least height of ditto, Jan. 6th, 1768 14. August 23, 1765, ex- 

 posed the thermometer, at noon, to the sun, suspended on a thread between two 

 sticks, in the middle of his garden at Caen, which may be about 2 English acres, 

 so that the thermometer received the least reflected heat possible in that place ; 

 the quicksilver stood as follows, at l** p. m. 97°, at 2^ ditto 96. August 26, 

 1765, at a village, called les Isles Bardelles, 7 leagues from Caen, the same 

 thermometer, in a south room, from which thesun was excluded by the window 

 shutters, rose to 90°. 



j4n /Account of a remarkable degree of cold observed at Caen in Normandy. 



li lU iUf'-' 



