Study of the New York Obelisk as a Decayed Boulder. 141 



November, 1881 

 December 

 January, 1882 

 February 

 March 



90°-in° F. (50°-62° C). 

 94°_109° F. (52°-t;i° C). 

 86°-106° F. (48°-59° C). 

 72°-110° F. (39°-61° C). 

 76°-117° F. (42°-65° C.)- 



It therefore appears that, even during the coolest season at 

 Thebes, the surface of solid bodies must be subjected to daily 

 variations of temperature approaching 72° to 117° F., i.e., about 

 100° F. every day. Also, from the table of maxima already given, 

 that a surface of stone is daily heated for a time, during eight or 

 nine months of the year, to a temperature at or above that of melt- 

 ing paraffin (146° F.). So far then as concerns mere oscillations in 

 temperature, the climate of Egypt must be far more trying to the 

 surface of stone than that of New York; the Obelisk, since its 

 transfer to New York, has been in much less need of protection 

 from injury by mere variations of heat and cold; and its sudden 

 decay immediately after its arrival here was certainly not due to 

 this agency. 



This subject has been here considered and discussed in some 

 detail, on account of the divergence of my conclusion from the 

 common view, and of its practical bearing on the true cause of 

 injury to building-stones, as well as to the Obelisk, to be feared 

 from our climate, and on the proper method for their protection. 



We have also invaluable evidence, already presented, as to the slow 

 action of even the burning sun of Egypt, as well as of its extreme 

 diurnal changes of temperature, upon the surface of granite, in the 

 condition of all the obelisks and of their sides which faced the mid- 

 day and afternoon sun (paragraph 8, (4), b), during recorded periods 

 of enormous length. 



18. Waterproofing treatment of other Egyptian obelisks. 



We may here pertinently refer to processes adopted abroad for 

 the protection from the weather of other Egyptian obelisks of the 

 same granite, and to the scanty testimony concerning their results. 



(1). The London Obelisk. — This monolith, once the fallen com- 

 panion of our own at Alexandria, reached the Thames, January 20, 

 1878, and was re-erected on September 12 of the same year. As 

 to its condition on arrival. Prof. Bartlett, of London, has stated in 

 a letter : " Soon after it arrived in the Thames, I was requested to 

 examine its then condition, and to advise a professional friend at 



