312 Royal Institiitioji. 



lecture would not be the exhibition of new and successful experi- 

 ments, but the indication of trains of scientific research, in which at 

 present all is doubtful and difficult, and in which the only light 

 which seems likely to guide us may possibly lead us in the wrong 

 direction. He then pointed out the difference, as it appears to be 

 usually understood, between knowledge and science, that the former 

 of these terms implies only the collection and careful arrangement 

 of accurately observed facts, while the latter implies in all cases the 

 idea of causation, and usually a reference to mechanical causes of a 

 simple kind, whose complexity of action depends upon the specialities 

 of distance, mass, &c. of the bodies upon which they act. This di- 

 stinction was illustrated by the state of astronomy, which before the 

 time of Newton was merely a collection of empirical rules, and after 

 that time became a science (the most perfect that is known) by re- 

 ference of movements to gravitation as a mechanical cause ; and by 

 the theory of light, which before Fresnel's time was a collection of 

 facts only, but after that time, when the facts were explained by 

 undulations (which are necessarily the effect of mechanical laws), 

 became a true science. The same distinction was applied to the 

 collections of statistical facts and the science of political ceconomy, 

 the moral causes in this science being analogous to tlie mechanical 

 causes in the physical sciences. In these cases it was not to be sup- 

 posed, nor was it possible, that we had come to the first cause ; 

 every general cause to which we could refer might itself be the sub- 

 ject of a more general cause : it suffices for us that we have gone 

 as far back as perhaps our nature permits. Applying these views to 

 terrestrial magnetism, it was to be said that terrestrial magnetism is 

 not at present a science; and the particular object of this lecture 

 was to point out what efforts had been made to bring it to the state 

 of a science, and in what direction we ought probably now to direct 

 our efforts, and with what prospect of success. 



Passing over the notorious fact of the direction of the magnetic 

 needle, the lecturer showed, by simple experiments, that terrestrial 

 magnetism is not an absolute, but a directive force (having no ten- 

 dency to move the magnet bodily, either north or south), and that 

 the poles of opposite nature of two magnets attract each other, and 

 that the poles of similar nature repel each other : and he insisted on 

 the advantage of using terms like austral and boreal, not too closely 

 connected with north and south, to express the kinds of magnetism 

 residing in the south and north poles of the earth, considered as a 

 magnet, and in the north and south poles of a free needle. He then 

 pointed out that the observation of the time of vibration of a magnet 

 might be made subservient to the determination of the proporlion oi' 

 the magnitudes of the horizontal magnetic force at different points of 

 the earth ; and expressed his regret that the mathematical character 

 of Gauss's beautiful and most valuable method for forming an abso- 

 lute measure of the force, entirely independent of the magnet em- 

 ployed, prevented him from offering it to the audience. _^The dip or 

 inclination of the needle was then described, and its general law (the 



