1851.] The adaptation of the Aneroid for surveying in India. 329 



in the cistern. Had due precautions been used, the results, would 

 most likely have been all in favor of the aneroid. 



The following were then tried at Parell Hill — first at the point where 

 the road from the gardens crosses ; then in the turret at the base of 

 the flagstaff. Barometer No. 4, which was left below stood at 29.960 

 at a quarter to seven : the observations were all made betwixt this and 

 half- past seven. 



No. 2 No. 3 No. 5 



Barometer, lower 29.940 29.920 29.916 



Barometer, higher 840 .828 .830 



Difference .100 .092 .086 

 giving a difference of elevation of about 90 feet. The aneroids stood 

 as follows, the instruments being arranged in the same way as before ; 



Road Station, 29.885 29.850 29.910 



Flagstaff, 815 .740 .815 



Difference .070 .110 .095 

 giving a mean of .092 nearly : a singularly close coincidence indeed, 

 the barometers in both cases having got heated in the sun, and no 

 time to allow the mercury to cool to the temperature of the attached 

 thermometer. The following ratings made at the observatory betwixt 

 the great standard and an aneroid are for two motives still more satis- 

 factory as being more full from May till December ; the discrepancies 

 are so great that they can only be explained on the assumption of the 

 instrument having got out of order. We have taken no account of the 

 difference betwixt the instruments, as they may be so adjusted as to 

 work together, the daily range being the great test of delicacy. 



