364 Mr A. J. Adie on the Expansion of Stone 



of the instruments for similar operations ; but Lieutenant Mur- 

 phy informed me, that he thinks it was employed in some py- 

 rometric operations connected with a trigonometrical survey in 

 India ; and I am satisfied, from the uniformity of temperature it 

 maintains in the instrument, no better method of heating can be 

 resorted to for such operations, because the substance, if of 

 wood or stone, is kept dry, and the fire or lamps are placed at such 

 a distance as not to incommode the operator in the least degree. 

 Some of the rods of stone experimented on are now before the 

 Society. I had considerable difficulty in making rods of Roman 

 cement, as they repeatedly cracked in drying, and I was anxious 

 to have this substance tried, as I found that rods of lime were 

 too weak, not more to settle the general question, as to the ex- 

 pansion of buildings, than to have the pleasure, if possible, of as- 

 sisting Mr Brunel, in accounting for the results of some experi- 

 ments he mentioned at the last meeting of the British Asso- 

 ciation, when describing one of the many beautiful contrivances 

 for which his fertile ingenuity has rendered him so celebrated. I 

 succeeded in making a rod of Roman cement, by at first mixing 

 as little water with the powder as would make it work, and when 

 it had become too plastic, from continued working, more of the 

 powder was added, and the cement again made plastic by work- 

 ing and beating. This process was continued so long as any of 

 the cement in powder could be added to the mass, and the whole 

 again worked into the consistency of soft putty, without any ad- 

 dition of water, as the strength of the mortar appears to de- 

 pend on the smallness of the quantity of water with which we 

 can make the dry powder plastic, this is accomplished by long 

 continued working. After preparing the mortar, it was put into a 

 mould of Bristol board, and when it had set, it was immersed in 

 water, and left for a fortnight to harden. 



Having ascertained that all the parts of the pyrometer worked 

 well from the uniformity of the results I obtained in determin- 

 ing the expansion of cast zinc, which was selected as the metal 



