NATURAL PHILOSOPHY. 265 



plant itself was high. From what he had described, it would be seen that 

 tiic land must contain an immense amount of water before the shallow drain 

 would operate. Where there were two sets of drains, one shallow and the 

 other deep, the shallow drains would be useless except to introduce air into 

 the soil. It should, however, be observed that if the soil were sufficiently 

 deep, drains might be placed at too great a depth. Since drainage had be- 

 come so general, millers in many parts of the country complained of the 

 want of water. This was owing to the level of the water being brought to a 

 point at which it was useless to fill the ponds. Draining one field, also, 

 would have the effect of draining the neighboring land, and if there were a 

 large area of the same kind of land, gravelly soil, for instance, one large 

 drain would suffice to drain the land for twenty miles round. The distance 

 at which drains should be made, must depend upon the nature of the soil. 

 If the soil were loose and gravelly, they might make the drains as far apart 

 as they chose ; but if the land were stiff and close, then they should make 

 the drains as near together as they could afford. 



ON THE VESICULAR THEORY OF MIST. 



A paper has recently been presented to the French Academy by the Abbe 

 Hailland, which denies the truth of the vesicular vapor theory concerning 

 clouds, and contends that the phenomenon in question depends on minute 

 divisions. As gold, when beaten into leaf, falls slowly, so the more the sur- 

 faces of water are increased, the more slowly will the water fall. The resist- 

 ance of air to a drop divided into a thousand parts, is a thousand times 

 greater than to a single drop. Hence clouds are borne up by the friction of the 

 atmosphere. That clouds should consist of vesicular vapor is, in the abbe's 

 opinion, simply impossible ; for if it were vesicular, it would be condensed ; 

 and if air were contained within the vesicles, the viscosity of the husk or shell 

 would have to be something very different from that of water. 



M. de Tessan, an eminent French meteorologist, has also published con- 

 clusions to the same effect. 



ESTIMATION OF SPECIFIC GRAVITY. 



M.M. Vogel and Reischauer recommend the use of a flask with a flat- 

 tened bulb for the purpose of estimating the specific gravity of liquids that 

 are much affected by change of temperature. With such a flask the equali- 

 zation of temperature is effected with much greater facility than in a flask 

 of the ordinary form. This flask is filled and emptied by means of a pipette 

 of equal capacity, with a long thin beak. The neck of the flask is graduated, 

 each division representing a known fraction of the volume of the flask. By 

 this means it is not requisite to remove any liquid from the flask by filter 

 paper. In order to derive full advantage from the shape of the flask, it is 

 necessary, on account of the uncertainty of reading off, that the neck of the 

 flask should be very narrow, otherwise the advantage in observing the tem- 

 perature is lost, especially in the case of liquids, whose expansion is not 

 widely different from that of water. 



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