288 PHILOSOPHICAL TRANSACTIONS. [aNNO l/l/. 



off something of the whole weight of the body ; but as much as the body 

 loses, so much the water gains, over and above what was given it by its rising 

 on account of the immersed body. 



A body therefore that falls in a fluid is so far from making the fluid lighter 

 as it falls, that it makes it press more upon the bottom that sustains it, when 

 it is falling, than when it was at rest in the fluid. If the vessel of water be 

 long enough for the falling body to come to a uniform motion before it reaches 

 the bottom, the force impressed on the water under the body will make it 

 press the bottom, as much as if the body were actually at the bottom; the 

 body in that case losing all its excess of gravity above that of the water, and 

 the water gaining it. 



Hence it follows, that a falling cloud, when it comes to a uniform motion, 

 will not only add to the weight of the air as much as the weight of an equal 

 bulk of air ; but even as much as its whole weight amounts to, though it be 

 specifically heavier than the air about it. 



All the diminution of weight that can be allowed in this case is this: if we 

 imagine the air to have a smooth, regular surface, as we have at first supposed, 

 (or if that be not allowed, we may take any imaginary surface of it above the 

 clouds) when a falling cloud is diminished in bulk, as when it is changed into 

 rain, the surface of the air will subside in proportion to that diminution, and 

 therefore will weigh less, by so much as is the weight of a quantity of air equal 

 to the bulk that cloud has lost: but when the drops of rain, after their accele- 

 ration (occasioned by their excess of gravity above that of the air) are come to 

 a uniform motion by the resistance of the air, they restore to the air the 

 weight that it had lost. Now this uniform motion being acquired in about 2 

 seconds of time, and the diminution of gravity in the air being insensible, when 

 compared to near 3 inches of mercury, (for such is the variation of the baro- 

 meter with us) it can nowise be the occasion of such sensible alterations in it, 

 as happen sometime before rain or fair weather. Add to this, that the whole 

 quantity of rain that falls in England and France, in the space of one year, 

 scarcely ever equals two inches of Mercury : and in most places between the 

 tropics, the rains fall, at certain seasons, in very great quantities, and yet the 

 barometer shows there very little or no alteration. 



An Account of an extraordinary Effect of the Colic. By M, St. Andre, 



N°351, p. 580. 



The peristaltic motion of the intestines is by all anatomists supposed to be 

 the proper motion of those cylindrical tubes. The use of this motion is to 

 propel the chyle into the vasa lactea, and to accelerate the grosser parts of the 



