376 Dr. Matthiessen on the Unit of Electrical Resistance. 



Before a.d. 1800. 100,000 Eccentricity. 00473 



90,000 „ 0-0452 



80,000 „ 00398 



70,000 „ 0-0316 



60,000 „ 0-0218 



50,000 „ 0-0131 



40,000 „ 0-0109 



30,000 „ 0-0151 



20,000 „ 0-0188 



10,000 „ 00187 



Epoch „ 0-0168 



After a.d. 1800. 10,000 „ 00115 



20,000 „ 0-0047 



30,000 „ 00059 



In round numbers, during these 130,000 years, the eccen- 

 tricity varied from 0'05 to - 005; therefore its square varied from 



0-0025 to 0-000025, or from. ^ to 4 q Q00 ' 



In equation (3) unity represents the total annual heat received 

 from the sun when the earth's orbit is circular, and \e 2 repre- 

 sents on the same scale the increment due to eccentricity ; hence 

 the total heats per annum received at the epoch 100,000 before 

 a.d. 1800, and receivable at 25,000 after a.d. 1800, are to 

 each other as 



1 + JL to 1 + 



800 * 80,000 



or as 80,100 to 80,001, showing an amount of change of -g-^th 

 between the epochs. 



This change of quantity of heat is very considerable, and capa- 

 ble of producing important results ; but whether it is capable of 

 producing a so-called " glacial epoch " would be difficult to say. 

 I am, yours respectfully, 

 Trinity College, Dublin, Samuel Haughton. 



April 16, 1866. 



LVI. Note on Dr. Siemens's Paper " On the Question of the 

 Unit of Electrical Resistance' 3 By A. Matthiessen, F.R.S* 



T is not ray intention to open a discussion on this subject, as 

 it has already been fully entered upon in the Reports of the 

 British Association for 1862-64. I will, however, point out 



* On applying to the Editor of the Philosophical Magazine to insert this 

 Note in answer to the paper which appeared in Poggendorff 's Annalen, 

 No. 2, 1866, he informed me that he had received from the author a trans- 

 lation of it for insertion in the present Number, and that therefore the 

 quotations had better be made from the English version. This I have done. 



