266 
POPULAE SCIEXCE EEYIEW. 
placed each in separate connexion with the electrometer, the intensity of the 
whole will not be greater than the intensity of one of the parts. A similar 
result ensues in charging any united number of similar and equal electrical 
jars. A battery of five equal and similar jars, for example, charged with a 
given quantity = 1, has the same intensity as a battery of ten equal and 
similar jars, charged with a C[uantity = 2 ; so that the intensity of the ten 
jars taken together is no gTeater than the intensity of one of the jars taken 
singly. In accumulating a double quantity upon a given surface divided 
into two equal and separate parts, the boundaries of each being the same, the 
intensity varies inversely as the square of the surface. Hence two separate 
ecj^ual parts can receive, taken together under the same electrometer indication, 
twice the quantity which either can receive alone, in which case the charge 
varies with the surface. Thus, if a given quantity be disj)osed upon two 
ec^ual and similar jars, instead of upon one of the jars only, the intensity 
upon the two jars Avill only be one-fourth the intensity of one of them, 
since the intensity in this case varies inversely as the square of the surface, 
while the quantity upon the two jars, under the same electrometer indication, 
will be double the quantity upon one of them only ; in which case the charge 
varies with the surface, the intensity being constant. If, therefore, as the 
number of equal and similar jars is increased, the quantity be also increased, 
the intensity will remain the same, and the charge will increase with the 
number of jars. 
Cry si allogenic Force. — Some observations concerning the phenomena 
displayed in the formation of crystals w^ere pointed out by M. Kuhhnann to 
the French Academy at its meeting on October 17th. This chemist experi- 
mented upon crystals of sulphates formed on glass, and from solutions which 
were thickened with gum. There was considerable difiiculty in preserving 
crystals prepared in this manner for the purposes of examination and com- 
parison. Hence the experimenter resorted to photographs and reproductions 
by means of the g'alvano-plastic method. By these means exact representa- 
tions were obtained. The only result of the faintest importance to which 
these inquiries lead is one which might easily have been anticipated — viz., 
that no two crystallizations can be obtained exactly alike. — See Gomptes 
Rendus, LIX., No. 16. 
Conditions under ivhich Air is carried doion hy a Stream of Water. — Mr. 
Eodwell, who contributed to a late number of the Philosophical Magazine a 
paper on the trompe, a hydro-pneumatic engine much in vogue upon the Con- 
tment, describes and enumerates the modes by which air can be carried down 
by a stream of water falling tlrrough a tube. These are four in number ; — 
1st. If the area of the cross section of the tube through which the water 
falls be not much greater than that of the orifice through which the water 
flows, disks will be formed in the tube, and, being pushed down by the 
descending stream, will force down the air beneath them. 
2nd. If the area of the cross section of the tube through which the water 
falls be much greater than that of the orifice from which the water flows, so 
that disk action is prevented ; or if the pressure on the lower end of the 
tube be competent to support a column of water in the tube, at such a 
distance from the orifice from which the water flows that the descending 
stream has not widened sufficiently to allow of the formation of disks, air 
