Fulton. — On the Fiji Fire-walkimj Ceremony. 197 



stone takes the greatest length of time to conduct from the 

 under to the upper surface enough heat to cause evaporation 

 or ignition, &c. Professor Park says, — 



I have made a series of experiments to determine conductivity and 

 rate of radiation, as requested by you, and the results are appended here- 

 with. To make comparative tests with skin or feathers would be diffi- 

 cult. 



Augite Andesite for Determination of Conductivity and Rate of Radia- 

 tion of Heat. 



Conductivity. — To determine the relative thermal conductivity of the 

 andesite a pencil of it was tested simultaneously with pencils of copper, 

 slate, and rhyolite, each pencil being 8 cm. long and - 5 cm. in 

 diameter. Taking the thermal conductivity of copper as equal to 1,000, 

 the relative conductivity of the others was found to be as follows : Slate, 

 7-63 ; andesite, 6-67 ; rhyolite, 2*35. From these figures it will be seen 

 that the highly acidic rhyolite is practically a non-conductor of heat, 

 while the conductivity of the others is very feeble. 



Radiation of Heat. — A series of experiments was made to determine 

 the relative rate of radiation of marble, rhyolite, andesite, basalt, and 

 cast iron. For this purpose a portion of each weighing 10 gm. (150 gr.) 

 was heated in a muffle furnace to a temperature of about 850° C. (about 

 1,562° F.) and then plunged for one second of time into a glass beaker con- 

 taining 100 c.c. of water. The portions of material were shaped so as to 

 give approximately an equal surface of radiation in each. The number of 

 degrees of temperature through which the water was raised was carefully 

 noted. In most cases the experiments were repeated three times, and in 

 all cases twice. The "means" of the different readings were taken, and, 

 expressing the radiation of iron as 100, it was found that the relative 

 rate of radiation of the others was as follows : Marble, 52 ; rhyolite, 50 ; 

 andesite, 48 ; basalt, 45. 



The experiments took many hours and the making of apparatus for 

 the tests. They seem to bear out your contention re feeble radiation of 

 the andesite — that is, the temperature might be very high, but, the rate of 

 radiation being so low, the heat given off in one second of time would not 

 be sufficient to burn the feet. 



From what I have said, and from Professor Park's experi- 

 ments, the results of which I have given, with his remarks 

 thereon, it seems to me that the fractured or inside surface of 

 this stone does not, owing to slow conductivity, receive nearly 

 the amount of heat one would expect. Secondly, owing to the 

 slow radiation of heat, also proved by these experiments, the 

 foot is not burnt when coming into contact with the stone for 

 a second or less. It would be interesting to have some of the 

 unsplit stones brought from Mbenga (Bega) to Otago and 

 heated to a temperature tbat would cause splitting and then 

 have the radiation from the two surfaces tested in some way. 

 This testing is hardly possible of application on the site of 

 the performance at Fiji, but would have to be carried out in a 

 properly equipped laboratory, as at the Otago School of Mines. 



My thanks are due to Dr. Marshall for his report on the 

 character of the stone, and I am much indebted to Professor 

 Park for the interest and trouble he took in the matter, and 

 for his kindness in devising and performing the tests, which 



