Tmi.rh/'irlge and Penrose — The Thomson Effect. 379 



rapid growth, but I think it safe to say that they will grow 

 i in fact old clearings are seen covered with trees of 

 second growth." 



F. G. Weidner, Surveyor General of Sinaloa, is authority 

 for the statement that the annual rain -fall at Culiacan in 1870 

 was 23 inches; in 1880, at Mazatlan, the chief seaport of 

 Sinaloa, it was 35 inches, and in 1881 an exceptionally wet 

 year, it reached the quantity (estimated) of 60 inches. It is 

 remarkable that across the Gulf of California, namely, in the 

 peninsula of Lower California, the rain-fall seldom reaches four 



Art. XLIII. — r,,,,/, //,>//,„„. /,,„„ //„ Physical Laboratory of 

 Ho rot,;! ChUoje. The Thomson Effect; by JOHN TROWBRIDGE 



and Charles Bingham Penrose. 



Sir William Thomson f first discovered that when an 

 iugh a piece of metal, the ends of 

 which are of different temperatures, it carries heat with it ; the 

 'hivctiou depending upon the character of the metal and the 

 direction of the current. This phenomenon is known as the 

 Thomson Effect. Le Eoux^: subsequently verified Thomsons 

 results, and gave an incomplete table of the effect in different 

 In, 't;ils. No especial pains have been taken hitherto in experi- 

 menting with pure metals. We have therefore thought it 

 would be valuable to test the effect in as pure a metal as we 

 i.v electrolysis. We have also extended Le Roux's 

 table by the addition of the effect in nickel, which Thomson 

 was unable to obtain, and also in carbon. An endeavor has 

 been made to ascertain if the effect is reversible, and also to 

 discover if it is modified in a magnetic field. 



The strip of nickel, 45 centimeters long, 2*6 wide, and 2 

 rs in thickness, was placed with its flat surface hori- 

 zontal. One face of a thermopile was placed at a fixed point 

 on the surface of the nickel, separated from it by a thin piece- 

 of mica. A weight pressed upon the other surface. The ther- 

 mopile was connected with a Thomson's reflecting galvanome- 

 ter of six ohms resistance. The two extremities of the strip of 

 nickel were connected with a battery of six Grove cells, the 

 wires first passing through a key so that the direction of the 

 current could be reversed. One end of the nickel was kept at 

 i he Natural and Mineral Resources of 



• Trans., 1856, 





