80 COSMOS. 



solstice the greatest western elongation, without the tempe- 

 rature of the atmosphere or of the earth's crust evincing a 

 maximum or minimum at these turning periods. Compare 

 the second volume of the Observations made at Toronto, p. 

 xvii, with the two treatises of Sabine, already referred to on 

 the Influence of the sun's vicinity (Phil. Transact, for 1850, 

 pt. i, p. 216), and of the solar spots (Phil. Transact, for 1852, 

 p. i, p. 121). 



The chronological enumeration of the progress of our 

 knowledge of terrestrial magnetism during half a century, 

 which I have uninterruptedly watched with the keenest 

 interest, exhibits a successful striving towards the attainment 

 of a twofold object. The greater number of these labours 

 have been devoted to the observation of the magnetic activity 

 of our planet in its numerical relations to time and space, 

 while the smaller part belongs to experiments, and to the 

 manifestation of phenomena, which promise to lead us to the 

 knowledge of the character of this activity, and of the 

 internal nature of the magnetic force. Both these methods 

 the numerical observation of the manifestation of terres- 

 trial magnetism, both in respect to its direction and intensity, 

 and physical experiments on the magnetic force generally, 

 have tended reciprocally to the advancement of our physical 

 knowledge. Observations alone, independently of every 

 hypothesis regarding the causal connection of phenomena, 

 or regarding the hitherto immeasurable and unattainable 

 reciprocal action of molecules in the interior of substances, 

 have led to important numerical laws. Experimental phy- 

 sicists have succeeded by the display of the most wondrous 

 ingenuity in discovering in solid and gaseous bodies polar- 

 ising properties, whose presence had never before been sus- 

 pected, and which stand in special relation to the tempera- 

 ture and pressure of the atmosphere. However important 

 and undoubted these discoveries may be, they cannot in the 

 present condition of our knowledge be regarded as satisfactory 

 grounds of explanation for the laws which have already been 

 recognized in the movements of the magnetic needle. The 

 most certain means of enabling us thoroughly to comprehend 



