METHODS AND RESULTS OF TORONTO OBSERVATIONS. 79 



the needle. It is to the continuous record thus obtained by 

 photography that we must look to obtain the information necessary to 

 establish the laws of change in the magnetic elements, and on the 

 occasion of violent magnetic storms they give us the means of com- 

 paring the most minute changes as well as the greatest, which on 

 these occasions seem to take place at the same instant of absolute time. 



Professor Grylls Adams has in this way investigated the great 

 magnetic storm of the nth, 12th. 13th and 14th August, 1880. 

 This storm began at 10 hours, 20 min., G. M. T. The traces show- 

 ing the same instant in Europe, Asia and America in high northern 

 and southern latitudes, and also near the equator at Bombay, and 

 everywhere precisely in the same way. A full report of the examina- 

 tions of the records of this storm will be found in the report of the 

 British Association for 1881, being a paper on magnetic disturbances 

 and earth currents by Professor W. Grylls Adams, F. R. S. 



Professor Adams says in closing his paper on magnetic disturb- 

 ances . '' We know so little as yet of the causes of the changes of 

 the sun, and this connection with terrestrical phenomena that we can 

 hardly do more than ask what possible causes there are that could 

 account for the effects which are observed. Can we suppose that 

 the sun is a very powerful magnet, and that a great alteration in his 

 magnetism accompanies the production of the bright faculce, and the 

 spots in his atmosphere ? Such a change of magnetism would affect 

 the magnetism of the earth, although the effect would not be large 

 unless the sun is magnetized to an intensity much greater than the 

 earth, even allowing for the difference in the mass of the sun and 

 earth." 



As I have already mentioned, Professor Balfour Stewart has 

 pointed out that there are similar periods of short range in the solar 

 spots and in the fluctuations of temperature at Toronto and other 

 stations where results have been worked up. 



The conclusion which he drew from these investigations was 

 that the sun emitted more heat at times of maximum number of 

 spots than at minimum. In order to test directly whether this was 

 the case he devised an instrument called an actinometer. One of 

 these instruments of a most improved pattern has been purchased 

 for use at the Toronto observatory. 



The instrument itself consists of a large mercurial thermometer, 



