[We are quite sure that our (tor-)Mentor is mistaken in assuming a uniform weight for the atmosphere.  It differs in different places.  During our lecturing-tours, we have frequently observed an involuntary depression of the eyelids (producing almost an appearance of sleep) in a part of the audience, which we were at a loss to attribute to anything but the weight of the atmosphere.  Water varies in the same way.  It is hardly necessary to say that Lake Wetter derives its name from the superior quality of its dampness.]

“2.  Of the specific gravity of the air he seems to be amusingly uncertain,—­making it first 833 times and afterwards 770 times less than that of water; and in the same connection he says, in chosen phrase, that ’density, or closeness, is another quality of the atmosphere,’—­as if it were its characteristic, and not common to all ponderable matter.”

[A very neat way of arriving at specific gravity in its densest form is to distil the “funny column” of a weekly newspaper.  To arrive at the desired result in the speediest way, let the operation be performed in what is known among bucolic journalists as a “humorous retort.”  Density and closeness should not be spoken of as equivalent terms.  The former is a common quality of the human skull, rendering it impervious; whereas a man may be very close and yet capable of being stuck,—­with bad paper, for example.]

“3.  In mentioning the constituents of the atmosphere, he adopts without explanation the loose statement of some of the books, placing carburetted hydrogen on the same footing as to constancy and amount with carbonic acid, and making no allusion to nitric acid.  Yet chemistry has shown, that, except in special localities, carburetted hydrogen occurs only as a slight trace, the existence of which in most cases is rather inferred than actually demonstrated, and that it has no important office to perform,—­while nitric acid shares with ammonia in the grand function of the nourishment of plants.  In a later paragraph the error is aggravated by the assertion, that ’no chemical combination of oxygen and nitrogen has ever been detected in the atmosphere, and it is presumed none will be,’—­as if every flash of lightning did not produce a notable quantity of this compound, which, washed down by the rain, may be detected in almost every specimen of rain-water we meet.  What would Johnstone, Boussingault, Liebig, and the other agricultural chemists say to this?”

[For complete proof on this head, be struck by lightning.  For ourselves, we are convinced, and would rather have some other head taken for an experiment by way of illustration.  But any of our readers who is unsatisfied has only to place himself in front of a lightning-express-train with an ordinary conductor.  To insure being struck, let the experimenter provide himself amply with patent safety-rods.  At least, this result is pretty sure in houses, and is worth trying out of doors.]