164 LIEUT.-COLONEL SYKES ON THE ATMOSPHERIC TIDES 



tions, when the arrival of other hygrometers from Europe permitted me to resume 

 them. 



Daniell's hygrometer I found to be an admirable instrument, ingenious in its con- 

 struction, definite and uniform in its indications, simple in its use, and satisfactory in 

 its results. But it is not without a drawback upon its utility. Independently of the 

 demand for a constant supply of aether, there are periods of the year in Dukhun 

 when the high temperature and extreme dryness render the dew-point only obtain- 

 able at such an expense of aether as to render it an object of pecuniary considera- 

 tion ; and with the very best aether I have never been able to reduce the tempera- 

 ture more than 61° of Fahrenheit's scale, that is to say, from 90° to 29°, on the 16th 

 of February 1828, at 4 p.m.; and at that hour the attempt in the months of March and 

 April 1827 proved fruitless, and I was obliged to give up a register of the dewing- 

 point in the afternoon. In the month of January, at sunrise, on the 4th and 6th 

 respectively, I got the dewing-point at three degrees below that of congelation of 

 _water, namely at 29°, the temperature of the air being 62° ; and on the 3rd of Febru- 

 ary 1828, the dewing-point was at 28° Fahr., the air 56°, at sunrise. On the 

 17th of February the lowest dewing-point ever registered was obtained, namely 27° 

 Fahr., temperature of air 57°'50 at sunrise. The objections, therefore, to this 

 instrument are, the great expense of aether in the dry months, and the occasional in- 

 ability to obtain the dewing-point when the temperature is very high and the day 

 very dry. I never had any difficulty in Bombay or in the Konkun in obtaining the 

 dewing-point, even at a temperature of the air of 91°'50 Fahr., nor will the effi- 

 ciency of the instrument ever be doubtful within the tropics near to the sea shore. It 

 is necessary to mention that the temperature of the air in Dukhun sometimes exceeds 

 the boiling-point of good aether. 



The measure of the quantity of rain which fell was taken with two instruments, 

 one of which was sent to me from Calcutta under the apposite name of ombrometer, 

 and the other was obtained from the medical stores at Bombay with the hybrid ap- 

 pellation of pluviometer attached to it. A hollow cylinder closed at one end had a 

 metallic float with gage-rod, resting on the bottom. The rain was received into a 

 round funnel fixed to the top of the cylinder: the diameter of the mouth of the funnel 

 was in a certain ratio to that of the cylinder, and this ratio regulates the length of 

 the inches on the gage-rod. The ombrometer was made of brass, neatly finished. 

 The pluviometer, of lackered iron, large, rudely finished, and unwieldy ; and it had 

 further the disadvantage (unlike the ombrometer) of its funnel-shaped mouth not 

 closing round the gage-rod, an improvement preventing the evaporation of the water 

 that falls into the instrument. Both rain-gages stood more than three feet high, 

 but their cylinders were of diff'erent diameters. In both, the inches on the gage-rod 

 were so large as to admit of hundredths (and even thousandths if it were required) of 

 an inch of water being read off with ease. They always worked very well together, 

 the only discrepancy being in the larger instrument indicating two or three hun- 



