1821.] . Bicarbonate of Ammonia, i ,n;\^ 111 



of lime are equivalent to 21*16 of ammonia. One hundred parts 

 of this salt consist, therefore, of 



Carbonic acid 55*5 



Ammonia 21* 16 leaving for 



Water 23-34 



100-00 



99-22 100-0 



The exact composition and atomic constitution are as follow, 

 and perfectly similar to the salt obtained by exposing what is 

 usually termed subcarbonate (but correctly sesquicarbpnate) of 

 ammonia to the air. i r . li ^ : 



Two atoms of carbonic acid 55*08 55-5 



One atom of ammonia 21-5 21*7 



Two atoms of water 22-64 22-8 



'- -^ Article VII. : 



On Rain-Guages, By Mr. Richard Davenport. > 



(To the Editor of the Annals of Philosophy.) 



SIR, Jan, 10, 1821. 



I PERCEIVE in your last number another letter added to the 

 many that have appeared on the subject of the different indica- 

 tions of similar rain-guages differently situated. It is rather 

 surprising that the writer should not before have met with the 

 observation that a greater quantity of rain falls on a given area 

 on the surface of the ground than on an equal area at a consi- 

 derable height above it ; it being notice.d and accounted for in 

 elementary books and lectures on meteorology generally. 



It is more surprising that disputes should have arisen and 

 have been carried on from time to time in a scientific publica- 

 tion, whether, on a given area, an equal or a smaller quantity of . 

 rain drops would be received if falling obliquely, than when fall- 

 ing perpendicularly, c^/^emj?rtri6?/s; it being a subject of easy 

 demonstration, and probably by the greater part of your readers 

 perceived to be so, although some of the disputants seem to 

 continue in their first error. 



There is, however, a cause of the different indications of simi- 

 lar rain-guages under the circumstances that have led to the 

 discussion, which I have not seen any where noticed, and it is 

 for this reason I trouble you with this letter. ^ 



If we suppose raiu drops to proceed at uniform relative dis- , 



