General results from our measurements of specific heat

General Results from Our Measurements of Specific Heat—In dealing with the form which the law of Dulong and Petit has assumed in the light of recent theory, we shall frequently be concerned with considerations of molecular theory, which are foreign to our particular subject. Nevertheless, it will be necessary for an understanding of our Heat Theorem to deal briefly with recent views on the subject of specific heats the results obtained with the vacuum calorimeter described in the previous chapter have not been without influence on their development. 

At the present time it may be put forward as a view which is experimentally justified, and is supported by the recent theoretical developments of physics, that the specific heats both of crystalline and of amorphous solids assume negligibly small values at very low temperatures. 

The idea that the atomic heats of all solid, i.e. non-gaseous, substances without exception become very small at very low temperatures, is first found developed in the paper presented by me on the 23rd December, 1905, to the Gdt-tinger Gesellschaft der Wissenschaften, which also contains the first presentation of my Heat Theorem. I there arrived at the result, directly contradictory to all earlier ideas, that the heat of evaporation at low temperatures always rises first, reaches a maximum, and then, and not until then, exhibits the usual decrease according to the First Law this means that the specific heat falls off rapidly at very low temperatures. The equation 

In the Silliman lecture (1906) I next showed that this limit must be between o and 2, and I made calculations, using the value 1 5, which, as I pointed out, was selected only preliminarily. 

Next appeared the paper of Einstein (vide infra) in 1907, 

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