This, of course, leads us to think of the ether as a carrier of light, heat, etc., and of how it can carry heat to the earth without becoming heated itself, as there can be no doubt about its being a material substance. How it can bring what may be called considerable heat to the earth and still have little or no heat in itself; even should it turn out, which we do not believe possible, that the estimates of the heat of space of -150° and -142°, made about the beginning of this century by Sir John Herschel and Pouillet, turn out to be near the truth. We have seen, in "Nature" of July 15, 1886, a monograph by Captain Ericsson, in which he shows that the heat radiated by the sun to where his rays strike our atmosphere is somewhere about 83°F., and it is not easy to see how radiated heat can be transmitted through 90 million miles of space at a temperature of much lower than -225°, and reach the confines of our atmosphere with the heat of 83°F. There is one supposition that occurs to us under which this can happen, and that is, that the sun only radiates heat to bodies which can receive it, and does not radiate it into all space where there is nothing but the ether to hold it. This, of course, implies that the ether acts the same part--the part for which it was really invented--with respect to heat that a telegraph wire does with respect to electricity; in which case, we could imagine that it starts from the sun with the maximum heat radiated by him, and that this goes on decreasing in the ratio of the square of the distance it travels through, the same as is understood to be the case with all radiated heat; and that the part of space not occupied, for the time necessary, by these connexions might be supposed to form the return current which we believe must exist, just the same as the earth does for electricity. For that there is a return current is demonstrated by the fact that the earth radiates heat into space when the sun is not shining upon it. Again, even in this case, we have another difficulty thrown upon us, over and above that cited by Captain Ericsson, of the heat delivered at the bounds of our atmosphere being about 83°F., by our being informed in "Engineering" of December 4, 1885, that: "A hot box, contrived to observe the temperature which could be attained by the unconcentrated solar rays, was used on Mount Whitney, 12,000 feet above the sea"--well within the limits of our atmosphere--"and that the enclosed thermometer rose to 233·3°F. on September 9, 1 p.m., 1881, the shade thermometer then reading 59·8°F." How are we to comprehend these two facts? We have seen a way of getting over part of the first fact as far as to the boundary of our atmosphere, but from there we have to carry 83°F. to the top of Mount Whitney, through the atmosphere there and present it along with the other lot in the hot box at 233·3°F.