IRODUCTORY LECTURE ON EXPERIMENTAL PHYSICS. 



progressive change going on, the cause of which is entirely unknown. In each 

 of the magnetic observatories throughout the world an arrangement is at work, 

 by means of which a suspended magnet directs a ray of light on a prepared 

 sheet of paper moved by clockwork. On that paper the never-resting heart of 

 the earth is now tracing, in telegraphic symbols which will one day be inter- 

 preted, a record of its pulsations and its fiutterings, as well as of that slow 

 but mighty working which warns us that we must not suppose that the inner 

 history of our planet is ended. 



But this great experimental research on Terrestrial Magnetism produced 

 lasting effects on the progress of science in general. I need only mention one 

 or two instances. The new methods of measuring forces were successfully applied 

 by Weber to the numerical determination of all the phenomena of electricity, 

 and very soon afterwards the electric telegraph, by conferring a commercial 

 value on exact numerical measurements, contributed largely to the advancement, 

 as well as to the diffusion of scientific knowledge. 



But it is not in these more modern branches of science alone that this 

 influence is felt. It is to Gauss, to the Magnetic Union, and to magnetic 

 observers in general, that we owe our deliverance from that absurd method of 

 estimating forces by a variable standard which prevailed so long even among 

 men of science. It was Gauss who first based the practical measurement of 

 magnetic force (and therefore of every other force) on those long established 

 principles, which, though they are embodied in every dynamical equation, have 

 been so generally set aside, that these very equations, though correctly given 

 in our Cambridge textbooks, are usually explained there by assuming, in addition 

 to the variable standard of force, a variable, and therefore illegal, standard of 

 mass. 



Such, then, were some of the scientific results which followed in this case 

 from bringing together mathematical power, experimental sagacity, and manipu- 

 lative skill, to direct and assist the labours of a body of zealous observers. If 

 therefore we desire, for our own advantage and for the honour of our University, 

 that the Devonshire Laboratory should be successful, we must endeavour to 

 maintain it in living union with the other organs and faculties of our learned 

 body. We shall therefore first consider the relation in which we stand to 

 those mathematical studies which have so long flourished among us, which deal 

 with our own subjects, and which differ from our experimental studies only in 

 the mode in which they are presented to the mind* 



