88 On a Ncn: Thconj of the Tides. 



observatory for instance) where the complication attending the 

 other would render it quite inapplicable. 



5. If we use the numbers formerly noticed for a and A, and 



put U) = 2-3 troy grains ; then — — = -0233, or -^^ nearly ; 



and ^^^ = -26, or \ nearly; and the formulae (2) and (3) 

 will become 



— ll 



■^ "" ^ 40 ' 



It 



y = m- — . 



These expressions are very simple and easily remembered. 

 If to the scale of the evaporating thermometer another scale 

 were attached, showhig the maximum tensions at the various 

 degrees of temperature ; or one showing the maximum quan- 

 tities of humidity in a cubic foot at the same temperatures ; we 

 should only have to deduct -^-^^ of the observed depression to 

 have the actual tension sought, or \ of the same quantity, to 

 have the actual quantity of vapour in a cubic foot. As St 

 will always be confined to a few degrees, a small table con- 

 taining the quantities to be subtracted might be engraved apart 

 on the scale of the instrument. 



The purpose of these observations is to explain the method 

 proposed by Dr. Hutton for finding the moisture of the atmo- 

 sphere on its own principles, and to disengage it fi'om all me- 

 chanism foreign to it. The process requires nothing more 

 than two thermometers which We have supposed to be con- 

 structed according to the centigrade scale. It is greatly to be 

 wished that a number of experiments were made sufficient for 

 ascertaining the practical fitness of the method for accom- 

 plishing its end. -, ■, 

 *^ ^ J. Ivory. 



XVII. On a New Theory of the Tides. By Capt. Forman, 

 of the Royal Navy. 



To the Editors of the Philosophical Magazine a7id Journal. 



Gentlemen, — If the facts and arguments contained in the 

 following letter are true, they must add to our stock of know- 

 ledge, and ought to be made known ; if they are not, they can 

 easily be refuted ; and therefore, as in either case they can do 

 no harm, I shall feel obliged if you will find room for them in 

 your Magazine. I am, gentlemen, &c. 



W. Forman. 



To 



