180 



Dr„ J. S. Lombard. On the Propagation of 



of minute bubbles of air will be fatal to successful experimenting. 

 The pile and bone thus constitute a single piece. 



The next step is to isolate, as far as possible, the whole pile from 

 all external thermal influences, except such as act through the piece of 

 bone, or through the conducting wires of the pile. To effect this, the 

 pile is enveloped in its whole length, and beyond to a distance along 

 its conducting wires of several times its length, in layers of fine 

 cotton-wool, which latter are afterwards steeped in melted paraffine. 

 The casing thus formed extends laterally beyond the edges of the 

 surface of the bone to which the face of the pile is attached. The 

 first layer of cotton- wool is applied loosely, and the paraffine is com- 

 paratively cool when poured upon the wool. The result of this is that 

 the paraffine does not penetrate very deeply into this first layer, thus 

 leaving a mass of loose wool, next the pile, entangling a certain 

 amount of air, and this latter furnishes a strong safeguard against 

 external influences. Of course, care must be taken that the attach- 

 ment of the face of the pile to the bone be not broken by the heat of 

 the paraffine. When all is complete the whole arrangement consists of 

 a mass of paraffine-soaked cotton-wool some 60 millims. in length, one 

 end of which is terminated by the piece of bone which protrudes from 

 the centre of this end,* while from the other end emerge the conduct- 

 ing wires of the pile, the pile thus forming the core of the mass, and 

 being shut off laterally and at its upper end from the exterior by 

 from 20 to 40 millims. of envelope. 



Two narrow strips of pasteboard, bound tightly by means of strips 

 of flannel, on opposite sides of the mass, near its upper end, and 

 brought together and tied so as to form a sort of arch above this end, 

 furnish a handle by which the mass can be held vertically, with the 

 exposed bone downwards, by the claw of a horizontal arm working up 

 and down a perpendicular metallic rod fitted into a small but steady 

 stand placed on the table, which supports the vessels containing the 

 water, and the thermometers and thermo-electric appliances used in 

 testing the differences of temperature between the air and the liquid. 



Brain and Shin. 



The fundamental principle was — as has been said — the same here as 

 in the case of bone, but, as the substances could not with safety be 

 brought into immediate contact with the water, the following special 

 arrangements were adopted : A box of thin pasteboard 50 millims. 

 deep by 85 millims. square was used as a mould, and was filled with 

 melted paraffine. After solidification had taken place, a space was cut 



* One must be sure that the paraffine does not extend down the sides of the piece 

 of bone so as to touch the water when the under surface of the bone is brought in 

 contact with the liquid, — as paraffine will conduct sufficiently well to introduce 

 errors into the results if the above precaution be not taken. 



