472 Scientific Intelligence, Sfc. 



electrified, which dust seems to he attracted from the circumambient 



air. 



" Now we know that the rain, even in our hottest days, comes 

 from a very cold region. Its falling sometimes in the form of ice 

 shews this clearly ; and, perhaps, even the rain is snow or ice when 

 it first moves downwards, though thawed in falling; and we know 

 that the drops of rain are often electrified ; but these causes of ad- 

 dition to each drop of water, or piece of hail, one would think, 

 could not long continue to produce the same effect : hence the air 

 through which the drops fall, must soon be stripped of its previously 

 dissolved water, so as to be no longer capable of augmenting them. 

 Indeed, very heavy showers of either, are never of long continuance, 

 but moderate rains often continue so long as to puzzle this hypo- 

 thesis. So that, upon the whole, I think as I intimated before, that 

 we are yet hardly ripe for making one.'' 



Notwithstanding this cautious remark of Franklin, it is obvious, 

 that in his time, the ripeness was quite equal to what it is at pre- 

 sent, as his hypothesis was founded upon the decisive observations 

 of Dr. Heberden, Cavendish, and others, in the year 1766. 



VI. — Constant Voltaic Battery. 



Professor Daniel, of King's College, exhibited his battery on the 

 6th inst. at the Royal Institution. He was led to construct this 

 very beautiful apparatus, by following up the investigations of Davy 

 and Faraday. He found that the protecting power of tin on cop- 

 per sheathing, was due to a chemical action. Thus he placed a plate 

 of silver in a solution of sulphate of copper; and on touching it 

 with a fine-pointed rod of zinc, he found the copper deposited on 

 it in a circular form, and in a regular manner ; and, if the contact 

 was kept up, the whole plate was supplied with a copper coating. 

 The effect of protecting metals appeared, at first, an objection to 

 the chemical theory of electricity ; but this experiment demonstrates 

 its truth. To determine and measure the definite chemical action of 

 electricity, Mr. Daniel has constructed a dissected battery. It con- 

 sists of ten cylindrical glass vessels, which contain the fluid electro- 

 lytes ; the two plates of metal are immersed in these fluids, each 

 plate communicating below by means of a separate wire, which is 

 made to perforate a glass stopper closing the bottom of the cell, with 

 a 3mall quantity of mercury contained in a separate cup below the stop- 

 per. The plates consisted of amalgamated zinc and platinum; the elec- 

 trolyte consisted of 100 water, and 2-25 sulph. acid. He found that by 

 increasing the size of the platinum plates, the action was promoted, 

 and that the zinc might be reduced to the size of a wire, with the 

 same effect as when a plate was used. Iron answers in place of the 

 platinum, but not instead of zinc. The dilute acid described, has 

 little action on the amalgamated zinc, because the latter becomes 

 speedily covered with bubbles of hydrogen, which mar its action. — 

 When nitric acid is added, the plate is soon dissolved, without ex- 



