310 



Uiil'ity of the Sympiesometer 



[Oct. 



able supporting powers, as I frequently observed the Sympiesometer to 

 fall when the wind changed, and to resume its former level when this 

 returned to its old quarter. I had intended to have discussed the ob- 

 servations with more detail, had time permitted, by the construction of 

 diurnal barometric and sympiesometric curves, with the registered 

 heights for their ordinates, and the hours of observations for their ab- 

 scissae, but, before I could have done this satisfactorily, and before the 

 series could be available for purely philosophical purposes, certain cor- 

 rections must have been applied, which it was not in my power to do ; 

 this paper is, therefore, merely intended to give an estimate of the 

 practical utility of this instrument, and the opinion I entertain of it is, 

 that, by itself, it is not of so much importance, but that, worked with 

 the barometer, giving as it does the very information this withholds, I 

 certainly think it a most valuable addition to our list of marine instru- 

 ments. The original construction of the Sympiesometer must however be 

 good, otherwise it is not to be depended upon, and I am inclined to think 

 much of the prejudice which has arisen: against it among naval men 

 takes its origin from the patent having been invaded, and cheap, and 

 inferior articles having been manufactured, and sold. From my own 

 observations I am most favourably impressed in regard to it, and should 

 always like, in every ship, to see the barometer and Sympiesometer 

 lending their aid to correct and strengthen each others indications. The 

 deductions from the table of observations may be condensed into the 

 following general rules, it being taken for granted that the barometer 

 and Sympiesometer are observed together, since this is, we repeat, the 

 only method whereby the greatest benefit can be derived from their 

 indications in guiding the commander of a vessel as to the weather he 

 is to prepare for. 



1. The steady simultaneous rising of the two, or their retaining 

 together a permanently high position, presages good and fair weather. 



2. Their simultaneous depression indicates a change to bad weather ; 

 if they fall very low, a heavy gale, usually accompanied with rain, may 

 be expected. 



3. If during the continuance of a gale, however violent it may 

 be, at the moment of observation, the two exhibit a decided 

 tendency to rise, the force of the storm will soon abate, its maximum 

 point being passed. If the Sj^mpiesometer, in consequence of its greater 

 susceptibility of slight variations in the atmospheric pressure, rises 

 alone, not so much confidence is to be placed in the hope that the storm 

 13 abated : — such rising is however a good sign, as it was usually soon 

 accompanied by a rise of the mercury in the barometer. 



