MEMOIR OF DR. WALKER. 31 



to think that we had now the altitude of the moun- 

 tain with as great exactness as it could be taken by 

 the barometer. 



" We at the same time put the thermometer into 

 boiling water, and after repeated immersions, it was 

 observed to stand constantly at two hundred and 

 thirteen degrees. The thermometer employed was 

 one constructed by Professor Wilson at Glasgow, 

 and we were therefore assured of its accuracy. The 

 water carried to the top of the mountain was from 

 a pure perennial spring on the shore of Jura ; and 

 the water of the same fountain was employed in 

 the repetition of the experiment. 



" From these experiments, therefore, it appears 

 that a column of air of the height of this mountain 

 is equal to two inches and six-tenths of mercury. 

 And assuming Dr. Halley's calculation of ninety 

 feet for each tenth, the perpendicular height of the 

 mountain turns out to be 2340 English feet above 

 the surface of the sea, which is just three hundred 

 feet less than half a measured mile. 



" The difference of the heat of boiling water, at 

 the summit and at the bottom, appears from these 

 experiments to be equal to six degrees of Fahren- 

 heit's thermometer; and the height of the moun- 

 tain, divided by this number, gives three hundred 

 and ninety feet for each degree." 



The following is the Report which he 'made to 

 the Society for propagating Christian Knowledge, 

 concerning the state of the charity schools in the 

 Highlands and Islands 



