656 Miscellaneous. [Dec. 



For iron raised to a full red heat, (1,200°, according to Prinsep,) 1,436,990°-=- 

 1,200° = 1,197.5 times, by using Prinsep's degrees. 



For do. raised to an orange heat, 1650° P. 1,436,990-H, 650=870 times by ditto. 



Reply to 3rd Question. 

 I almost fear to venture an opinion on the next question, but 1 should say, that 

 the atmosphere is certainly, as the querist supposes, attracted, by the sun and 

 moon, when in conjunction, or opposition, in the same manner, as are the tides of 

 the ocean, or as any other light fluid, would be ; but why the barometer is not 

 sensibly affected, at these periods, I can only ask, whether he is sure that it is not 

 so affected, or so much, at least, that a fair conjecture may be hazarded, that its 

 rise is proportional to the increased height of the atmosphere, (if such indeed 

 occur, at the time of high tides,) : our purpose will, therefore, be to see, whether the 

 barometer can indicate this rise, or not, and if it do, to determine, what the 

 amount of that difference is. 



May not one objection however be made, that will have a tendency to controvert 

 this opinion, which is, that the force, exerted by the moon or sun, or both, to 

 elevate the atmosphere, above its usual level, might, on account of the elasticity, 

 or buoyancy of this body, destroy the additional weight, that would, otherwise, be 

 added to it? In other words, would not the force of attraction, here supposed to 

 cause the additional height, by the hold, (if I may say so,) that it has on the fluid, 

 keep it in equilibrio, without adding any thing to the weight, by the increase of 

 the part so added ? 



This remark will not, of course, apply to water, but will it not to air, which is 

 an elastic body ? If not, then I must resort to the first supposition, that there is a 

 rise of the barometer, and that it is proportional to the increased height of the 

 atmosphere, caused by the attraction of the sun and moon. 



If the height of the atmosphere were uniform, and of the same weight, as it is at 

 the earth's surface, pressing about 14£lbs. on the square inch, it would extend no 

 farther than to the height of 5f miles, or thereabouts, (see Hutton's Course, p- 

 244, vol. ii.) whereas it reaches to between 40 and 50 miles, (the boundaries of 

 twilight only included, the air being so thin and attenuated, beyond that distance, 

 that its comparative weight amounts to almost nothing). 



Now, if the height of the atmosphere be increased, by any cause, (excluding 

 heat, which would, however, have something to do with that increase, but has or 

 has not to do with this investigation,) beyond the height of 45 miles, a propor- 

 tional part must be reduced, in height, on the sides of the earth, which are at 

 right angles to the horizon, acted upon by the sun and moon, to make up for 

 this quantity, unless it be rarefied and of itself kept in equilibrio by attraction, as 

 above supposed : it cannot be very great, but supposing it to be proportionally 

 raised, as much as the sea, what will be the pressure gained, in this, upon one 

 square inch, at the surface of the earth, and also, at what height will the baro- 

 meter stand, in this case ? 



Taking 12f feet, which is about the height of the tides, or what is added to the 

 ocean, by the attraction of the sun and moon, either when in conjunction or oppo- 

 sition, and assuming J of a mile, or 1760 feet, as the average depth of the 

 ocean, of which 12f feet is near the 138th part ; by taking the 138th part of the 

 atmosphere's height of 45 miles, as above, we get .326087 parts of a mile for the ad- 

 ditional height of the atmosphere, gained by the force of attraction, consequently, if 

 45 miles press upon the surface, with a weight of 14| lbs. per square inch, 45.326,087 



