174 MR THOMAS HEATH ON 



The Annual Curves. 



Complete tables of the whole of the observations made with the old set of rock 

 thermometers during the forty years from 1837 to 1876 inclusive will be found in 

 Volumes XL, XII., XIII. , and XIV. of the Edinburgh Astronomical Observations. 

 This set of thermometers was erected at the Calton Hill in 1837 at the expense of the 

 British Association for the Advancement of Science. At the same time two other sets 

 were put up by the Association, one in the sandstone rock of Craigleith Quarry and 

 another at the Experimental Gardens, now part of the Botanic Gardens. All three sets 

 were established chiefly at the recommendation of the late Prof. J. D. Forbes. The 

 two sets at Craigleith Quarry and at the Botanic Gardens were regularly observed for 

 five years, and the results, along with those of the Calton Hill set for the same five 

 years, are to be found in an interesting paper by Prof. Forbes, published in Vol. XVI. 

 of the Transactions of the Royal Society of Edinburgh. The destruction of both these 

 valuable sets of instruments appears to have taken place soon after the five years' 

 observations had been secured. The Craigleith thermometers were maliciously destroyed 

 in May 1842, and the set at the Experimental Gardens was broken by a storm in the 

 winter of 1844-5. The sole remaining set, that in the rock of the Calton Hill, existed 

 complete up to 1861, when t 2 , or the second deepest thermometer, was found broken off 

 at the surface of the rock during the severe frost of the winter of 1860-61. The 

 remaining three of this set were destroyed in September 1876 by an unfortunate 

 Portuguese sailor, whom, on his arrest by the police, it was found necessary to place in a 

 lunatic asylum. 



A complete description of the construction and erection of these thermometers, and 

 a discussion of the method of determining the corrections of their readings, will be found 

 in the paper by Prof. Forbes mentioned above, where he further discusses the results of 

 the observations, and deduces the mean temperatures for the five years, the rate of 

 increase of temperature with depth, and the ranges at different depths, showing how 

 these depend on the varying conductivity of the strata at the three stations. The 

 forms of the annual curves are then discussed, and their equations determined for each 

 of the four thermometers at the three stations. The curves are shown graphically in a 

 plate, and from these curves the epochs of maximum and minimum temperatures were 



obtained by interpolation. To obtain the value of the ratio /-, where k is the con- 

 ductivity of the soil and c the specific heat, Prof. Forbes makes use of the equation 

 log. A =A + Bp, where A is the therm ometric range at a depth p in French feet, A 

 and B constants, of which B is always negative. The determination of these constants 

 Prof. Forbes looked upon as the primary object of his investigation. A is equal to the 

 logarithm of the thermometric range at the surface, or where p = 0. B determines the 

 rate of diminution of the range below the surface, being smaller as the heat descends 

 more readily, or as the conductivity is greater. This coefficient B was shown by 



