444 Professor Elias Loomis. 



facts about storms. But even the method he then used was 

 entirely unfitted to give answers to the questions which mete- 

 orologists were asking. Some of those questions were stated in 

 circulars issued by the joint committee of the American 

 Philosophical Society and the Franklin Institute : What are 

 the phases of the great storms of rain and snow that traverse 

 our continent ; what their shape and size ; in what direction, 

 and with what velocity do their centers move along the surface 

 of the earth ; are they round, or oblong, or irregular in shape ; 

 do they move in different directions in different seasons of the 

 year? 



The graphic representation by Professor Loomis on the map 

 of the United States of the storm of 1836 had been a series of 

 lines drawn joining the places where at a given hour the 

 barometer was at its lowest point. That line would so far as the 

 barometer was concerned mark for that hour the central line of 

 the storm. The progress of the line from hour to hour on the 

 map showed, quite imperfectly, how the storm had traveled. 

 Some arrows added showed to the eye also certain facts about 

 the movements of the air. 



Professor Espy adopted and thereafter adhered to a modifi- 

 cation of this method of representing storm phenomena, and I 

 think meteorologists will agree with me in my opinion that 

 Professor Espy's four Reports from 1842 to 1854 though they 

 contained an immense accumulation of facts, were because of 

 this radical defect of presentation almost useless to meteorolog- 

 ical science. 



In the discussion of the storms of 1842, instead of the line 

 of minimum depression of the barometer, Professor Loomis 

 drew on the map a series of lines of equal barometric pressure, 

 or rather of equal deviations from the normal average pressure 

 for each place. A series of maps representing the storm at 

 successive intervals of twelve hours were thus constructed, 

 upon each of which was drawn a line through all places 'where 

 the barometer stood at its normal or average height. A 

 second line was drawn through all places where the barometer 

 stood -^ of an inch below the normal ; and other lines 

 through points where the barometer was -^ below, T 6 7 below, 

 y 8 ^ below, etc.; also lines were drawn through those points 



