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



source of heat, a flat charcoal stove or upright pan, 20 by 14 inches 

 in dimensions, with its face covered by coarse wire-grating, ke)>t 

 filled with charcoal at red heat. This stove was suspended usually 

 at a distance of about 25 inches from the marked spot on the east 

 face. In order to direct and control a uniform heat upon this spot, 

 the stove was partly surrounded by a sheet-iron screen, extending 

 from the stove to the surface of the rock. 



The degree of surface temperature was determined by another 

 thermometer, whose bulb lay against the same marked spot. It 

 was controlled b}^ moving the stove occasional!}'' back and forth, 

 when the ignited charcoal varied a little in radiated heat, as on the 

 addition of fresh fuel, so that the temperature should remain at 

 about 88° C. (190° F.) ; it ^\i;as found to be under easy control, 

 within a few degrees, with the apparatus described. The experi- 

 ment began at 11 A.M., on Tuesdav, Julv 20, 1890, in charge of 

 both members of the Committee, and continued for 1^ hours until 

 sunset, the thermometers being constantly observed and noted. 

 The day happened to be very suitable for the experiment, clear 

 and warm, the temperature during the afternoon varying from 25° 

 to 21° C. ; the air was nearly calm, with only now and then a very 

 light breeze, which was continuous after 5 P. M. At any time 

 during the experiment, the observer could without discomfort lay 

 his hand on the warmed surface of the rock, alongside of the ther- 

 mometer. With constant and careful inspection of the surface, 

 during the heating and at its close, "no evidence whatever was 

 seen of cracking, scaling, or any other injury to the warmed .stone" 

 on the east face, or on its section on the north face. 



(2). The application of melted paraffin. — To the spot on the 

 east surface of the boulder, warmed for i\ hours as just described, 

 melted "paraffin, colored red by alkanet root, was applied with a 

 brush for a few minutes, before the sun went down and brought 

 this experiment to an end. The reddened paraffin was found to 

 have penetrated at least 1.7 centimeters (f of an inch), even with 

 so short an application." 



"During that experiment, however, another stove was applied 

 in the same way to a neighboring boulder of the same stone, of 

 smaller size, during two hours. To this spot a shallow metal tank 

 was taken quickly and tightly fitted, with its side open against the 

 warmed rock, and filled with the same colored paraffin, kept liquid 

 for one hour longer. The tank was then removed, and, on the next 

 day, the face of the rock was cut off and the depth of penetration 



