324 REPORT — 1851. 



forms of clouds and to facilitate their notation on the journal, in accordance 

 with the nomenclature adopted by meteorologists. 



"The following collection of tables, to be used in reducing the observations, 

 has been prepared by Professor Guyot at the expense of the Institution : — 

 Thermometrical Tables. 

 Barometrical „ 



Hygrometrical „ 

 Hypsometrical „ 



" Besides these it is proposed to furnish a set of tables for determining 

 heights by means of the barometer. We may also mention, in connexion 

 with this subject, that a series of preliminary experiments have been made in 

 the laboratory of this Institution for the purpose of constructing from direct 

 observation a scale of boiling temperatures corresponding to different degrees 

 of rarefaction of the air. With a thermometer, each degree of which occu- 

 pies one inch in length of the scale, the variations of the boiling corresponding 

 to a slight change in altitude are found to be more perceptible than those of 

 variations in altitude of the barometrical column. A series of experiments 

 has also been made for testing the performance of the aneroid barometer 

 under extremes of atmospheric pressure. The instrument, however, has not 

 been found from these experiments very reliable, though it may serve as a 

 baryscope or an indicator of atmospheric changes. It will by no means 

 serve for the determination of atmospheric pressure, particularly when sub- 

 jected to ranges of considerable magnitude. 



" For the better comprehension of the relative position of the several places 

 of observation now embraced in our system of meteorology, an outline map 

 of North America has been constructed by Dr. Foreman. This map is in- 

 tended also to be used for presenting the successive phases of the sky over 

 the whole country as far as reported to us at different epochs, and we have 

 been waiting for its completion by the engraver to commence a series of 

 investigations with the materials now on hand relative to the progress of 

 storms. 



" A valuable collection of returns relative to the aurora has been received 

 in accordance with the special instructions which we have issued for the 

 observation of this interesting phasnoraenon. These are to be placed in the 

 hands of Capt. Lefroy of the Toronto Observatory, and incorporated with 

 observations of a similar kind which he has collected in the British Posses- 

 sions of North America. Abstracts of the whole series will be presented 

 by Capt. Lefroy, to be published in the Smithsonian ' Contributions to 

 Knowledge.' 



" The whole number of observers on which we may now depend, including 

 those of all classes, is about 200 ; these are, however, very irregularly distri- 

 buted over the face of the country. By far the greater number are in New 

 York and New England. We hope, however, to be enabled to enlist a 

 number of other States, and to carry out the plan more efficiently in behalf 

 of the Institution as soon as our income will warrant a larger expenditure of 

 means for this purpose. 



" The number of stations must be left to yourself*, and their distribution 

 had best be determined by consultation with Capt. Lefroy. I would, how- 



* [This paragraph was written in the belief entertained at the time by Professor Henry, 

 that the cooperation of the British Government would be asked to carry this system of ob- 

 servation over the whole of the North American Continent, by establishing corresponding 

 stations in the British portion. It appears, however, by subsequent communications, that 

 this request has been made, not to the British Government, but to the Governor of the Ca- 

 nadian Provinces.] — E. S., March 1852. 



