Cambridge Philosophical Society, 397 



4. In this part of the communication, attempts made by the author 

 to find the effects of various influences on electric conductivities of 

 metals are described. One of these, with a very unsatisfactory 

 method for testing resistances, led to the conclusion that longitudinal 

 magnetization diminishes the conducting quality of iron wire. The 

 general plan for testing resistances, which he subsequently adopted 

 as the best he could find, and which has proved very satisfactory, is 

 next explained ; and as an illustration, a single experiment on the 

 relative effect of an equal longitudinal extension on the resistances of 

 iron and copper wires is described. The conclusion established by 

 this experiment is, that both by extension with the tractive force 

 still in operation, and by permanent extension retained after a cessa- 

 tion of stress, the conductivity of the substance is more diminished 

 in iron than in copper ; or else that it is more increased in copper 

 than in iron, or increased in copper while diminished in iron, if it is 

 not in each metal diminished, as the author is led by a partial in- 

 vestigation of the absolute effect in each metal to believe. 



5. The result previously arrived at regarding the effect of longi- 

 tudinal magnetization on the conductivity of iron is confirmed ; and 

 an experiment that would have been found impracticable by the 

 less satisfactory method, proves the same conclusion for magnetized 

 steel wire, with the magnetizing influence away. Two very different 

 experiments show further, that the electric conductivity of magnetized 

 iron is greater across than along the lines of magnetization. A last 

 experiment, showing that iron gains in conducting power by mag- 

 netization across the lines of the electric current, leads to the con- 

 clusion that there is a direction inclined obliquely to the lines of 

 magnetization, along which the conductivity of magnetized iron 

 would remain unchanged on a cessation of the magnetizing force. 



CAMBRIDGE PHILOSOPHICAL SOCIETY. 



[Continued from p. 320.] 



Feb. 25. — A paper was read, " On a direct method of estimating 



Velocities, Accelerations, and all similar magnitudes with respect to 



Axes moveable in any manner in Space, with applications." By Mr. 



Hayward, of St. John's College. 



The frequent recurrence, in many different investigations of kine- 

 matics and dynamics, of exactly corresponding equations, suggests 

 the inquiry whether they do not result from some common principle, 

 from which they may be deduced once for all. An investigation 

 based on this idea forms the first part of this paper, and the result 

 is the method mentioned in the title. 



This calculus shows how the variations of any magnitude, capable 

 of representation by a straight line of definite length in a definite 

 direction, and subject to the parallelogrammic law of combination, 

 may be simply and directly determined relatively to any axes what- 

 ever. If such a magnitude (m) be estimated in a given direction, its 

 intensity in that direction will be represented by the projection on 



