372 ANNUAL OF SCIENTIFIC DISCOVERY. 



of the hour-angles, since the errors are common to both triangles 

 Z P S and Z P M, and both are augmented or diminished nearly 

 alike ; and therefore the ' difference ' between erroneous hour-angles 

 will be nearly equal to the difference between correct hour-angles." 



METEOROLOGICAL INFORMATION. 



THE following circular has been issued by the Smithsonian Institu- 

 tion. It is to be hoped that the call for information may be readily 

 responded to from all parts of our extensive territory. 



The Smithsonian Institution is engaged in a series of investigations 

 relative to the Meteorology of North America, and is desirous of col- 

 lecting all information bearing on this subject. 



It is believed that there exist many records of observations extend- 

 ing back, in some cases, through a long period of years, the compari- 

 son and discussion of which would elicit much valuable information 

 relative to the climate of this country, which would otherwise be 

 liable to be lost. The undersigned would therefore earnestly request 

 that copies of such journals, or the* original records, be lent or presen- 

 ted to the Institution. In cases of records which cannot be sent to 

 the Institution, monthly or other mean results deduced from them are 

 requested, with explanations of the manner in which the observations 

 were made, the character of the instruments, &c, 



Proper acknowledgment of all information derived from the 

 records will, in every instance, be given, and the registers themselves 

 will be carefully preserved, and returned, if desired, to those from 

 whom they were obtained. 



When it is recollected that isolated observations are greatly enhanced 

 in value, and made to yield new results by comparison with other 

 observations, it is hoped that the request of the Institution will meet 

 with favorable regard. 



EVAPORATION AND CONDENSATION. 



THE total quantity of dew believed to fall in England is supposed to 

 amount to five inches annually. The average fall of rain is about twenty-- 

 five inches. Mr. Glaisher states the amount of evaporation at Greenwich 

 to have amounted to five feet annually for the past five years, and 

 supposes three feet about the mean evaporation all over the world. On 

 this assumption the quantity of actual moisture, raised in the shape of 

 vapor, from the surface of the sea alone, amounts to no less than 

 GO, 000 cubic miles annually; or nearly 164 miles per day. According 

 to Mr. Laidlay, the evaporation at Calcutta is about fifteen feet an- 

 nually, that between the Cape of Good Hope and Calcutta averages 

 in October and November nearly, three quarters of an inch daily ; 

 betwixt 10 and 20 in the Bay of Bengal it was found to exceed an 

 inch daily. Supposing this to be double the average throughout the 

 year, we shall, instead of three, have eighteen feet of evaporation 

 annually ; or were this state of matters to prevail all over the world, 



