Study of the New York Obelisk as a Decayed Boulder. 143 



The extreme maxima reached were 151° F., on September 6, 

 1880. and 154° F., on September 7, 1881. The hours at which 

 the temperature in the sun reached its maximum are recorded for 

 each day in 1885, 1886, and 1887; from these we may conclude 

 that the maximum continues on an averag-e for about 1^ hours, or 

 perhaps somewhat less. If we assumed that the light colored sur- 

 face of the granite of the Obelisk reached on these days the same 

 temperature as that indicated by the bull) of the maximum ther- 

 mometer in the sun, which is not probable, we might infer that the 

 .surface of the monolith is occasionally heated to the temperature of 

 146° to 150° F. for short periods, which amount, on an average, to 

 less than five hours during the whole year. 



There is then no foundation for the fear, expressed by some 

 persons, that the paraffin, at that melting-point, may flow or has 

 already flown down from the surface to the base of the monument, 

 under the attack of our summer sun. It is more probable, so far 

 as the heat of the sun may ever cause the surface of the paraffin 

 to melt, that this will recement and solidify, during each summer, 

 the superficial minute cracks produced in the paraffin through con- 

 traction by the cold of the preceding winter. 



As to the intense heat of the Egyptian sun, there is abundant 

 evidence. Burckhart observed the temperature of the air at Esne 

 at 139° F., and Coutelle, that at Cairo at 127° F., and at Philse, 

 129° F.' Coutelle records a constant temperature at Fhilge, from 



1 Foissac, idem, II, 272. 



