538 



temperature ranging between 64 and 85* 7. In every instance it 

 was warmer, the greatest difference being 6'6. 



1 1 . Eleven observations of Valeriana tuberosa in comparison with 

 grass. 



The mean gives the Valerian 0'5 warmer than grass; the tem- 

 perature ranging between 52*6 and 73. In seven instances it was 

 warmer than the grass, the greatest difference being 3 0> 3. 



[In the last four examples the temperature at night, and the 

 maximum with black bulb are included, so that the former will tend 

 to lower the result and the latter to raise it.] 



XI. " Reduction and Discussion of the Deviations of the Com- 

 pass observed on board of all the Iron-built Ships and a 

 selection of the Wood-built Steam-ships in Her Majesty's 

 Navy, and the Iron Steam-ship ( Great Eastern';" being a 

 Report to the Hydrographer of the Admiralty. By FRE- 

 DERICK J. EVANS, Esq. Communicated by the Lords 

 Commissioners of the Admiralty. Received May 5, 1860. 

 (Abstract.) 



The analysis of the deviations of the compass in this paper com- 

 prises the observations made in forty-two iron ships, varying in size 

 from 3400 to 165 tons, a selection of wood-built screw and paddle- 

 wheel steam-vessels, as also the steam-ship * Great Eastern' at various 

 times prior to her departure from England. 



The observations made in the iron-built ships extend over periods 

 varying between thirteen and five years ; and having been made with 

 the same description of compass the Admiralty standard and under 

 similar conditions of arrangement and situation, in accordance with 

 the system carried out in Her Majesty's Navy, details of which are 

 given, the general results are strictly comparable. 



In the analysis of the Tables, amounting to nearly 250 in num- 

 ber, of deviations observed in various parts of both hemispheres, the 

 formula deduced from Poisson's General Equations by Mr. Archi- 

 bald Smith, given in the Philosophical Transactions for 1846, p. 348, 

 has been employed. 



In this formula, the deviation of the compass on board ship, 



