152 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



posite conclusions. Streintz's conclusions are that the elas- 

 ticity of a conducting wire is not affected when an electric 

 current is passing through it, except to an extent corre- 

 sponding to the temperature of the wire; that, however, on 

 the other hand, the length of a conducting wire is changed to 

 a considerable extent more than is due to the temperature, so 

 that it expands in its length from 15 to 25 per cent, more 

 than is due to the temperature to which it is heated by a 

 passing current. 



The experiments w^ere made upon brass, copper, soft and 

 hard steel, all the other metals giving results coinciding with 

 the previously stated law. The expansion in length of the 

 hard steel was not greater than might possibly have been 

 due to errors of observation. From certain conclusions, 

 Streintz conceives that the heat excited by the galvanic cur- 

 rent is polarized, a conclusion to which Villari was led by a 

 very different process of reasoning. It is notable that the 

 expansion due to galvanism seems to have no relation to the 

 modulus of elasticit}^ 19 C, 1873, 219. 



THE POWER OF SMALL TELESCOPES. 



De Abbadie gives some interesting details as to the degree 

 of minute visibility that can be attained by the use of small 

 astronomical telescopes. He says that Kitchner, in 1815, w^ith 

 a Ramsden telescoiDe of 2^jy inches' aperture, and a magnify- 

 ing power of seventy times, saw the companion star to Polaris. 

 A sliort time before the death of Dawes, that eminent En- 

 glish observer published, at the request of De Abbadie, some 

 of his own results. He says that a telescope of 1.6 inches' 

 aperture easily showed the companion of Polaris, and did 

 so even after its aperture had been reduced to 1.4 inches, 

 provided the heavens were particularly favorable to this 

 class of observations. De Abbadie's own experiments in this 

 direction were made with a telescope of 1.8 inches' aper- 

 ture, manufactured by Dallmeyer, of London. With a mag- 

 nifying power of thirty, this telescope shows the companion 

 of Polaris ; and with a magnifying jDower of seventy-eiglit 

 times, and a very steady atmosphere, he separates the north- 

 ern pair of the star Epsilon Lyrae. The previous observations 

 Avere made with English telescopes; but he says that this 

 perfection in the construction of small telescopes is not nn- 



