NATURAL PHILOSOPHY. 149 



the position occupied by the centre of the ball, and would continue to indi- 

 cate at each instant the actual atmospheric potential, however variable, as 

 long as no sensible electrification or diselectrification has taken place through 

 imperfect insulation or convection by particles of dust or currents of air 

 (probably for a quarter or a half of an hour, when care is taken to keep the 

 insulation in good order). This might be the best form of apparatus for 

 making observations in the presence of thunder-clouds. But I think the best 

 possible plan in most respects, if it turns out to be practicable, of which I 

 can have little doubt, will be to use, instead of the ordinary fixed insulated 

 conductor with a point, a fixed conductor of similar form, but hollow, and 

 containing within itself an apparatus for making hydrogen, and blowing 

 small soap-bubbles of that gas from a fine tube terminating as nearly as may 

 be in a point, at a height of a few yards in the air. With this arrangement 

 the insulation would only need to be good enough to make the loss of a 

 charge by conduction very slow in comparison with convective loss by the 

 bubbles, and it would be easy to secure against any sensible error from de- 

 fective insulation. If one hundred or two hundred bubbles, each one-tenth 

 of an inch in diameter, are blown from the top of the conductor per minute, 

 the electrical potential in its interior will very rapidly follow variations of 

 the atmospheric potential, and would be at any instant the same as the mean 

 for the atmospheric during some period of a few minutes preceding. The 

 action of a simple point is, (as I suppose, is generally admitted) essentially 

 unsatisfactory, and as nearly as possible nugatory in its results. I am riot 

 aware how flame has been found to succeed, but I should think not well in 

 the circumstances of atmospheric observations, in which it is essentially 

 closed in a lantern ; and I cannot see on any theoretical ground how its 

 action in these circumstances can be perfect, like that of the soap-bubbles. I 

 intend to make a trial of the practicability of blowing the bubbles ; and if it 

 proves satisfactory, there cannot be a doubt of the availability of the system 

 for atmospheric observations. 



ON THE EMPLOYMENT OF THE LIVING ELECTRIC FISHES AS MEDI- 

 CAL SHOCK MACHINES. 



Prof. George Wilson, in a paper before the British Association, Dublin, 

 stated that his attention had been incidentally directed to the employment 

 of the living torpedo as a remedial agent by the ancient Greek and Romar 

 physicians ; and he now felt satisfied that a living fish was alike the earliest 

 and the most familiar electric instrument employed by mankind. In proof 

 of the antiquity of the practice he adduced the testimony of Galen, Diosco- 

 rides, Scribonius, and Asclephiadcs, whose works proved that the shock of 

 the torpedo had been used as a remedy in paralytic and neuralgic affections 

 before the Christian era. A still higher antiquity had been conjecturally 

 claimed for the electric silurus or malapterurus of the Nile, on the supposi- 

 tion that its Arabic name, Raad, signifies thunder-fish, and implied a very 

 ancient recognition of the identity in nature of the shock-giving power and 

 the lightning force ; but the best Arabic scholars have pointed out that the 



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