412 COURSE AND LEVELS 



9. With regard to the elevations expressed in the Section a few of them 

 rest on Trigonometrical measurement as (already detailed), the others are 

 deduced from the following Table of Observations made of the temperature 

 of boiling water. The Thermometer I used was the largest procurable ; 

 it had a scale of 40° to an inch. The boiler was a copper vessel about twelve 

 inches in height and two in diameter. It was provided with a false bottom 

 at a height of three inches above the lower one. This was pierced with holes 

 and the water poured in till it reached to about three inches above it. The 

 thermometer was then placed in it so that the bulb was fully covered with 

 water. The reading was made with the assistance of a magnifier of about 

 five or six inches focus which was held quite out of the reach of the steam, 

 the vessel being always open and the steam quite unconfined. I had found 

 that any thing held over the mouth of the boiler even though it did not half 

 close it, had the effect of raising the temperature. But by boiling in the 

 manner I have described I had very consistent results. It will appear 

 perhaps a matter of regret that I had not the Thermometrical Barome- 

 ter described by Archdeacon Woollaston. This Instrument however is 

 not made of sufficient extent as yet to comprehend within its range the 

 boiling points given in the following Table. I mean without using the me- 

 thod of boiling and tapping as described by the inventor. This method 

 would have been of less easy application in a journey hurried as this neces- 

 sarily was from want of supplies, than in the easier journies through civiliz- 

 ed Europe. I can think of nothing which the common Thermometer 

 wants to render it perfectly adequate to these measurements, beyond some 

 enlargement of its scale, and a division into inches and decimals by a ver- 

 nier. One- fourth or even one- fifth of an inch to each degree would be am- 

 ply sufficient. 



10. In the following Table I have added a column shewing the corrected 

 result ; the manner of obtaining it will be explained a little farther on. 



