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Scientific Proceedings, Royal Dublin Society. 



is constant all the year round, and is (approximately) that of the 

 mean annual temperature of the locality. The actual depth of the 

 " invariable stratum " is found to vary in different localities, and 

 the stratum itself is necessarily thick, as the variations in tem- 

 perature alternate very slowly as we approach the position of no 

 variation. Observations for determining the depth of the stratum 

 have been made both at the Paris and Greenwich observatories. 

 At Greenwich it was found (in 1858) that the deepest of several 

 underground thermometers, 25 feet from the surface, showed a 

 range of variation amounting to 3 "42° Fahr., so that the stratum of 

 no variation lies at a greater depth than 25 feet. For the southern 

 parts of the British Isles, a depth of about 50 feet is, doubtless, a 

 sufficiently close approximation. 



The observations taken by Mr. Doran on the Ballynoe Springs 

 resulted in the interesting determination that the temperature is 

 constant, and that it is that of the mean annual temperature of the 

 locality, namely, 51° Fahr. The observations were carried on 

 throughout the month of March, a period of the year in which the 

 temperature of the air varies considerably ; and were twenty in 

 number. Observations on the temperature of the air were taken 

 at the same time, and are given in the following Table : — 



Observations on the Temperature of the Water of the Ballynoe Springs, 

 taken during the month of March, 1888. 



