322 Dr. M. Maclean. On the Effects of Strain 



The lines of the stars of intermediate temperature, like a Cygni, 

 have long been recognised by the Harvard observers as well as by my- 

 self as presenting great difficulties. 



In 1893 I wrote as follows* : " With the exception of the K line, 

 the lines of hydrogen aud the high temperature line of Mg at A.4481, 

 all the lines may be said to be at present of unknown origin. Some of 

 the lines fall near lines of iron, but the absence of the strongest lines 

 indicates that the close coincidences are probably accidental." 



In the Harvard ' Spectra of Bright Stars ' 1897, p. 5, the following 

 words occur, relating to the same stars : 



" This system of lines should perhaps be regarded as forming a 

 separate class, as in the case of the Orion lines, and should not be 

 described as ' metallic,' as has just been clone in the absence of any 

 more distinctive name." 



From the fact that these unknown lines have now been traced to a 

 " proto-metallic " origin, as effectively as the unknown lines of the 

 hottest stars have been traced to helium and asterium, we may expect 

 that the consequences of this determination in relation to stellar classi- 

 fication and other connected matters, will be very far reaching. At 

 present I am using this new spectrum consisting of enhanced lines as 

 an explorer, in relation to some further details of stellar classification 

 having special reference to stars of Groups III and IV in which bright 

 as well as dark lines occur. 



" On the Effects of Strain on the Thermo-Electric Qualities of 

 Metals." By MAGNUS MACLEAN, M.A., D.Sc. Communicated 

 by Lord KELVIN, F.RS. Eeceived January 23, Eead Feb- 

 ruary 2, 1899. 



1. Seebeckf discovered the great effect that hardness, or softness, or 

 crystalline structure, has on the thermo-electric properties of metals. 

 Magnus made a number of experiments by winding a hard drawn wire 

 on a reel. Parts of this wire were softened and annealed. When 

 heat was applied to the parts of the wire which were between unan- 

 nealed and annealed, a thermo-electric current was obtained. In this 

 way Magnus found that the current passed from soft to hard through 

 the hot junction for silver, steel, cadmium, copper, gold, and 

 platinum ; and that it passed from hard to soft through the hot junc- 

 tion for German silver, zinc, tin, and iron. 



2. Lord Kelvin describes in vol. 2 of his ' Mathematical and Physical 

 Papers ' a number of qualitative experiments to determine the direction 



* ' Phil. Trans.,' A, vol. 184, p. 694. 

 t ' Pogg. Ann.,' 1826. 



