14 The Value of Earth Temperatures. 



The present question is one of the greatest importance — it 

 alike affects the Astronomer, the Geologist, and the Agriculturist. 



I should have gone more fully into this enquiry, had it not been 

 that I understood my friend and colleague, the Curator of the 

 Museum, intended to read a valuable paper, and I therefore de- 

 termined to defer any detailed remarks I might have to offer 

 about Earth Temperature until a future occasion. Indeed, my 

 especial object in exhibiting these Earth Thermometers, is to 

 give the members of the Eoyal Society of New South Wales, an 

 opportunity of seeing them as they are, before they are buried 

 in the earth, 



I hastened to get these Earth Thermometers in action as soon 

 as possible, especially in consequence of a conversation that took 

 place, when I was examined before a select committee of the 

 Assembly, about the disease in Emit Trees, and its connection 

 with Meteorology. I was then asked what would be the law of 

 temperature at different depths below the earth's surface ; and 

 whether it would not be desirable to try experiments for the pur- 

 pose ? 



Although I had already written to England about these Earth 

 Thermometers, yet, I was so impressed with the importance of 

 immediate action, and also fearful about the risk of transit to a 

 Thermometer 20 feet in length, that I adopted — as I conceived — 

 the safer and more expeditious course of getting them from our 

 Sister Colony — Melbourne. 



But although I am certain that most valuable results will be 

 obtained from Earth Thermometers, at the same time, it is equally 

 certain that they should be made on a most extensive scale to be 

 of practical and scientific utility. I believe the great desideratum 

 should be to obtain localities as near as possible to the level of 

 the sea. There is my own Observatory, which is 155 feet above 

 the level of the sea, yet my deepest Thermometer will be 20 feet 

 only, and the same remarks must apply to Greenwich and Edin- 

 burgh. 



I have made these remarks especially with a view to guard 

 against any misconception as to the hypothesis that the law 

 of temperature will be the same in any locality whatever. Such 

 a condition is hardly attainable, and could hardly be expected. 



It is well to give an illustration of the subject of my discourse 

 this evening, and I have selected the observations made at Edin- 

 burgh, for the following reasons, viz : — 



1st. — They extend over 23 years, (from 1837 to 1859, inclusive,) 



2nd. — They give the greatest range of depth, viz., from 3 feet 

 to 32 feet. 



3rd — The Thermometers were actually constructed, and the 

 observations made (personally) by no less a philosopher than 

 Professor Eorbes. 



