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



" 4. That those decayed spots whose large area (sometimes reach- 

 ing a diameter of twenty inches), deeper hollow sound, and display 

 of cracks, indicate the depth of their decay and the possible exist- 

 ence beneath of a cleft or cavity of some size, shall be submitted, 

 immediately after two hours' warming, to the action of a tank of 

 melted paraffin for about an hour, or until there is evidence of the 

 arrest of absorption of paraffin. 



"For this purpose we also recommend the use of tanks of greater 

 height, in order to increase the hydrostatic pressure of the melted 

 paraffin and its consequent penetration into the interstices of the 

 rock. 



"5. We particularly recommend the careful treatment, in the 

 latter method, of the large loosened flakes upon the west face of the 

 pyramidion and vicinity, and of the southwest corner of the Obelisk 

 for thirty feet below, and that the cracks be left neatly filled up or 

 'pointed' with solid paraffin," 



20. Experiment on rate of penetration of heat into granite. 



For the practical end in view in the experiment described, the 

 rough estimate stated was entirely sufficient. But the figures 

 obtained were available for a closer determination of the rate of 

 penetration of the heat-wave, and this has been since calculated 

 and is now presented below. 



Before the experiment, the entire set of thermometers, Nos. 1 to 

 13, were carefully compared, in the part of the scale used (above 

 20° C), in warmed solutions at successively increasing tempera- 

 tures, with a pair of standard thermometers, made by Tonnelot, of 

 Paris, marked Nos. 50 and 52, kindly loaned to me for the purpose 

 by Dr. Charles F. Chandler. In these, the constants had been 

 already determined at the Yale College Observatory. The com- 

 parative trials were carried on in the Laboratory of Microbiology 

 of Columbia College, but need not be described in detail. The 

 results of the comparison yielded the following corrections, which 

 have been applied to all the observations recorded beyond. 



