NATURAL PHILOSOPHY. 91 



like the tail of a comet from the surface of the great reflector. Judging 

 from some recent experiments on the power of such a reflector to aug- 

 ment the intensity of the light emanating from its focus, there can be 

 no doubt that, along the axes of the cone, when brought to its narrow- 

 est limits, the illuminating force of the carbon light as displayed on the 

 State House could be rivalled only by that of several millions of can- 

 dles shining unitedly along the same line. 



In the above-described observations, a thick screen was necessary, on 

 account of the great intensity of the lights to be antagonized. I need 

 hardly say that the different color of the two lights added much to the 

 difficulty of the measurements. But, by marking in each case the ex- 

 treme limits on either side, it was practicable to adjust the screen pretty 

 accurately to equality of illumination. 



The only previous experiment, of precisely the same kind, which I 

 can recall is that of Bunsen, cited in the books, which was made with 

 a battery of forty-eight elements. In this, the photometric equivalent 

 of the carbon light was estimated at 572 candles, or nearly twelve 

 candles to the cell. My observations show a power more than three 

 times as great, or about forty candles to the cell ; a difference due no 

 doubt largely to the more intensive battery at my disposal and the 

 cumulative effect of its arrangement. I suspect, too, that the elements 

 in Bunsen's observation were of inferior size, but on this point I am 

 without definite information. 



ELECTRICAL SUMMARY. 



Electric Express. M. Bonelli, the Italian electrician, suggests a 

 new application of electricity for the transmission of letters, light parcels, 

 &c. A series of coils of insulated wire are adjusted along the route, 

 and through them runs a pair of rails upon which travels the wagon 

 which carries the despatch-box. This wagon also carries an electric 

 battery, and the end of the coils are so adjusted that the battery con- 

 nection is made, by means of the wheels and rails, through the coil which 

 it is just about to enter. As the wagon is of sheet-iron, it will be at- 

 tracted to the centre of the coil, and the momentum which it acquires 

 will carry it far enough to make the connection through the next coil, 

 when the impulse is renewed. 



This contrivance will make a very pretty philosophical toy, or piece 

 of illustrative apparatus ; but can it be economically applied on a prac- 

 tical scale ? Cosmos. 



Efficacy of Lightning Conductors. M. Quetelet, in commenting on 

 a remarkable thunder-storm that raged over a considerable part of 

 Belgium, in February, I860, states that, in his statistics of the buildings 

 or vessels struck by lightning, " he found that out of a hundred and sixty- 

 eight cases in which lightning-conductors had been struck, only twenty- 

 seven, by reason of grave defects in their formation, had failed to 

 exercise a preservative power." 



Influence of Heat on the Voltaic Battery. M. Carlo Roberti, of Ve- 

 rona, in a note forwarded to the Academy of Sciences at Paris, states 

 that, while pursuing some experimental researches with Gauss's appa- 

 ratus, he was struck first with the irregularity and afterwards with the 

 progressive periodical intensity of the pile he employed. He was soon 

 led^o attribute this to the variation of the temperature, due to the 



