1890.] President a Address. 473 



electrical experiments, and expressing theoretically the velocity of 

 propagation of an electro-magnetic disturbance, agreed within the 

 limits of error of experiment with the known velocity of propagation 

 of light ; and accordingly that we have strong reason for believing 

 that light is an electro-magnetic phenomenon, whatever the appro- 

 priate physical idea may hereafter prove to be which we ought to 

 attach to the propagation of an electro-magnetic disturbance. But as 

 yet no means existed by which phenomena, such as those of inter- 

 ference, which are bound up with the propagation of undulations, 

 could be exhibited by purely electrical raeans. Professor Heitz was 

 the first to detect electro-magnetic waves in free space by his inven- 

 tion of a suitable receiver, consisting of what may be called a 

 resonating circuit, which gives visible sparks when immersed in a 

 region of sufficiently intense electric radiation. 



By reflection, refraction, and interference experiments, he has 

 further verified the undulatory nature of the disturbance near a quick 

 electric oscillator, such as had been suggested by Professor Fitzgerald, 

 on the basis of Clerk Maxwell's electro-magnetic theory of light, and 

 Sir W. Thomson's theory of the oscillatory character of a Leyden jar 

 discharge. 



These important researches contribute powerfully to the induce- 

 ments we have to refer the phenomena of light and electricity to a 

 common cause, different as hitherto their manifestations have been ; 

 and by this means the theory of each may be advanced through what 

 we know of the other. 



One of the Royal Medals has been awarded to our Fellow, Dr. 

 David Ferrier, for his researches on the localisation of cerebral 

 functions. 



We owe to his experiments on monkeys, animals which he was the 

 first to use for this purpose, the beginning and indeed the greater 

 part of our knowledge of cerebral localisation in man. From patho- 

 logical observations, Broca located the centre for speech in the third 

 left frontal convolution, but with this exception nothing was known 

 of cerebral localisation in man until Dr. Ferrier commenced his 

 experiments in 1873. 



Fritsch and Hit/ig in 1870 had observed that definite movements 

 could be obtained by electrical irritation of the cerebral cortex in the 

 dog, and this indicated the existence of localised motor areas in the 

 brain. They did nothing, however, towards localising sensory centres, 

 and even in regard to the motor centres their observations were very 

 limited. Their experiments, moreover, were confined to dogs, and it 

 may be doubted whether any great or rapid advance would have been 

 made had not Ferrier hit upon the happy device of experimenting 

 upon monkeys, whose brains present a great similarity in the arrange- 

 ment of the convolutions to those of man. By employing these 



