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sciences as an example, and we at once see how this is. Take for 

 instance chemistry, compare it as it now is with what it was when 

 Priestley commenced his career. The whole of the science then con- 

 sisted of an imperfect knowledge of the properties of a few of the 

 metals, of sulphur, phosphorus, and the three alkalies as they were 

 then called. There was a little known also about salts and acids, and 

 the existence of hydrogen and carbonic acid gas had recently been 

 ascertained. In a range so limited there was little room but for one 

 master mind, when Priestley discovered oxygen, and at once an open- 

 ing was made for researches into the nature of the atmosphere, of 

 water, and of combustion, of the acids and the alkalies, and ample 

 employment was provided for a host of distinguished philosophers 

 for years to come. Other important discoveries were soon made, 

 each becoming as it were a new origin of light, throwing perhaps 

 at first but feeble rays upon the objects around us, but revealing so 

 much of their strange forms as to excite curiosity, and awaken the 

 strongest passion of the human mind, — the desire to discover the 

 truth. Inorganic chemistry was then rapidly becoming a great 

 science, when the foundations of organic chemistry were laid in a 

 succession of brilliant discoveries. That was but a few years ago, 

 but there were many men then ready trained for the work, and the 

 progress was proportionally rapid. To take a few of the disco- 

 veries in organic chemistry, and show how each has been the germ 

 of others, as it were the first term of a diverging series, and thus 

 to exhibit the great principle at work that in science labour creates 

 a demand for labour, might perhaps be of some interest, but it would 

 lead me from the object which I have in view, which is simply to 

 point out the grounds upon which I have ever felt a strong conviction, 

 that whatever means were placed at the disposal of the Royal Society, 

 no lasting difficulty could occur in turning them to useful account. 



During the last year considerable progress has been made by Mr. 

 Hopkins in the important experiments which he has been carrying 

 on in conjunction with Mr. Fairbairn and Mr. Joule. You no 

 doubt are aware, that, as we descend below the surface of the earth, 

 it has been found that the temperature increases : numerous experi- 

 ments made in different places with all the necessary precautions to 

 guard against fallacy, seem clearly to have established the fact. The 

 increase is about one degree of Fahrenheit for a depth of from 50 to 

 60 feet. If therefore the conducting power of the materials of the 

 globe was the same at all depths, we should have a series, which 

 would give us the depth proportional to every required temperature. 

 Reasoning in this way, we conclude that a temperature higher than 

 that of melting iron exists at a depth of thirty miles, and that at 

 double that depth the materials of the surface of the globe, combined as 

 we find them in nature, would enter into fusion. It has therefore been 

 supposed by many that the solid crust beneath our feet is not more 

 than forty or fifty miles thick. It has however been assumed that the 

 increasing pressure at increasing depths does not alter either the 

 conducting power of materials, or the temperature at which they 

 melt. This no doubt is to a certain extent incorrect, and it is highly 



