1851.] The adaptation of the Aneroid for surveying in India* 341 



Bap-dieu Ghat, August 23rd. 



Barometer I. Symp. Ther. 



Poona, 7 a. m 27.952 28.05 76 



Bap-dieu Ghat, 9 a.m. .... 26.747 26.85 74 



1.205 1.20 



The Barometer is corrected for temperature to 32°. 



The Barometer at the Colaba Observatory stood on the 23rd August 

 at 29.845 or 1.893 higher than that at Poonah : if to this be added 

 „030 for the difference betwixt 7 a. m. at which the upper instrument 

 and 10 A. m. at which the lower one was read, we shall have a differ- 

 ence of 1.923, or adding 3 for difference of elevation betwixt the Cola- 

 ba and Sewree Standard, almost exactly the same as that originally set 

 down as the result of the first comparison. At Poona the range be- 

 twixt the 26th, and 31st July was about .040, that at Bombay about 

 .070, that for the latter part of August at Bombay about .090 : I have 

 no note of the Poona range of this date, but assume it at 6, and have 

 taken the half. 



While in Poona I took with me three Aneroids with a Sympiesome- 

 ter into the carriage, and drove over the station to see with what faci- 

 lity the instruments could be employed in flying surveys. I did this 

 repeatedly. On one occasion I was accompanied by Col. Grant : on 

 another by Captain Stoddart : it is needless to give details — compared 

 with the barometer the coincidences were of course always wonderful : 

 oil one occasion we took a series of levelled stations, where the accu- 

 racy was surprizing. The great recommendation, both in their case 

 and that of the Sympiesometer, was the facility with which they could 

 be observed : by pulling up the horses for a couple of minutes the 

 scale could be read and marked at once, and one hundredth of an inch 

 being allowed for ten feet of change of level, which it is at this eleva- 

 tion pretty nearly, no reductions of any sort were requisite—these 

 could be performed at home afterwards. 



The following paper is by Professor Patton — it gives the merits of 

 the experiments, with the Aneroid up to 4500 feet : it has been pub= 

 lished in the Bombay Times and no where else that I am aware of. 



" Considerable discussion has of late arisen on the subject of the 

 Aneroid Barometer, and great uncertainty still exists in reference to 



2 y 2 



