220 On the Comparative action of Aneroid Barometers. [No. 3. 



Such falls varying from half an inch (0.50) to two and a half inches 

 (2.50), or even more, we know occur in the Tropical Cyclones,* and in 

 these the Thermometer is perhaps always between 75° and 80° ; and, 

 speaking of course theoretically, and from the diagrams of the instrument, 

 it has always appeared to me questionable what the action of an Aneroid 

 would be in one of our China Sea Tyfoons, or Bay of Bengal or 

 Malabar Coast Hurricanes ; that is, if it would equal the Simpieso- 

 meter, if it was even found to be as good as the Barometer as to time, 

 in warning of the approach of the Cyclone 1 and again if its index 

 would, at the height of the Cyclone, shew the same amount of dimi- 

 nished pressure ? A few very simple experiments by the instrument- 

 makers, or by Amateurs of physical research, who may have the 

 necessary apparatus, would solve this doubt; but the instrument-makers 

 are not likely to be desirous of checking the sale of a new and rapidly- 

 spreading article; and scientific men in Europe, unless they have 

 attended to the subject, have little conception of what a singular and 

 wonderful complication of meteorological phenomena a tropical Cyclone 

 in all its terrific power presents. f 



* I have given in the Sailor's Horn Book, p. 233, a table of excessive falls of 

 the Barometer in Cyclones comprising fourteen well attested instances of falls 

 from 2.70 to 1.50. 



f Ex. gr. In the Elements de Physique Experimentale et de Meteorologie of 

 Pouillet, fifth edition (1847) Vol. I. p. 142, we are gravely told that " Des 1690, 

 le Pere De Beze avait reconnu qu'a Pondichery et a Batavia le barometre reste 

 immobile, quelles que soient les tempetes que Ton eprouve : Legentil avait con- 

 firme ces observations ; et maintenant il est bien demontre que, dans toute la zone 

 equatoriale, le barometre est en effet insensible aux secousses atmospheriques, mais 

 qu' il eprouve cependant des variations periodiques et regulieres, que Ton appelle 

 variations horaires." 



As early as 1690 Father De Beze had found that at Pondicherry and at Batavia 

 the Barometer remains unaffected whatever tempest be felt. Le Gentil had con- 

 firmed these observations, and it is now well demonstrated that throughout the 

 equatorial zone the Barometer is really insensible to violent atmospheric dis- 

 turbances (secousses) but that it experiences regular and periodic variations which 

 are called hourly variations." M. Pouillet's name is, as most of my readers may 

 know, next only to that of MM. Arago and Biot as a Professor of Physics ; and 

 his work is the standard one in the University of Paris ! 



