146 Study of the New York Obelisk as a Decayed Boulder. 



The similar averages, at New York, for the remaining months of 

 1882, were as follows : — 



April 

 May . 

 June 



60 i October ... 30 



59 



38 



November ... 50 

 December ... 50 



These figures show that while the changes in the range of tem- 

 perature at New York are frequent and sudden, and correspondingly 

 trying from the physiological point of view, the actual daily ranges 

 of temperature at Thebes are 60 per cent, greater than those at New 

 York, constant, and proportionately severe in the amount of repeated 

 expansions and contractions of the surface of stone caused b}'^ such 

 daily oscillations. The ranges at Thebes do not lose in importance 

 from the fact that they occur somewhat further up the scale than at 

 New York, since the question of frost is a distinct subject for con- 

 sideration. 



A natural conviction as to the severity of our climate, with its 

 intense heats of summer, bitter cold periods during midwinter, and 

 frequent and sudden alternations of rains, snow, and sunshine, 

 thawing and freezing, during spring and autumn, has influenced 

 the popular judgment on the true causes of stone-decay. 



The common, and, as I think I have shown, mistaken view, 

 thereon upheld, may have been partly founded on inexact apprecia- 

 tion of the intervals between conspicuous extremes of temperature 

 at New York. Thus, in January, 1882, the observed temperatures 

 varied at one time from 97° F. in the sun to — 6° F. in the shade, 

 but with an interval of six days between these extremes, and no 

 greater range than 58° on any one of those days. At Thebes, in 

 the same month, the variation of 94° occurred on a single day (the 

 2d), viz., from 45° to 139° F. 



But the actual ranges of temperature to which the surface of a 

 solid body must have been subjected at Thebes, between the extreme 

 heat of the burning sun by day and the cold produced by radiation 

 toward the cloudless sky of Egypt by night, may be probably better 

 estimated with reference to the minima recorded at night by a 

 thermometer on the grass. From Hutcheson's tables for these 

 minima and for the maxima in the sun, I have deduced the follow- 

 ing variations of the daily ranges of temperature during each of the 

 same five months. 



