We confess that all these deductions have startled us, but we can see no flaw in the reasonings which have led to them. If it is not for want of ether--in sufficient quantity at least--and the admission of variable quantity is to admit that it is a material substance, that electricity will not pass through a highly exhausted tube, we cannot imagine what can be the reason why it does not; simply accepting it as a fact is by no means satisfactory. In the dilemma between renouncing the ether altogether or acknowledging its disappearance--effective at least--it occurred to us that it might be for want of heat, and that in terms of the inter-dependency of temperature and pressure in a gas, heat disappeared in proportion to the decrease of pressure in the air or gas that was being exhausted from the tube, or from cold being applied to it from without; but that notion has already been disposed of by our own work, when we have seen that a gas in a close vessel can be heated or cooled to any degree, altogether independently of pressure. When, acknowledging that the ether ought to have some temperature as well as density, we have said that it might have the temperature of vibration whatever that might be, thereby admitting that we could not pretend to determine what it is; nevertheless, we may take a look at it from a distance, and at least see what it cannot be, anywhere within the limits of our system. We have shown, at page 220, that when the original nebula was about 29,000,000 miles in diameter, its density must have been 0·179 that of air at atmospheric pressure, and its temperature -225°, and that these could be neither the density nor temperature of space. With this temperature, then, it is evident that there was still heat enough and to spare in the ether--considering it to be a material substance--to cause it to vibrate and perform its assigned offices; and, therefore, it could not be for want of heat that neither it, nor light, nor electricity could be carried through the vacuum tube, but for want of the ether in due quantity; consequently, the temperature of vibration cannot be so great as -225°. Turning back now to page 129, we find the density of the ether estimated at 1/5,264,800th of an atmosphere, which corresponds to an absolute temperature of 0·000052° or -273·999948°; but on the following page we expressed our opinion--well founded, we believe--that the estimate was too high, i.e. too dense, and that it might be 2, 3, or 4 times, or more, too great. Be this as it may, we can see that if the ether alone occupies space--beyond a comparatively very limited distance from any body belonging to the solar system--it must be almost absolutely free from temperature of any degree, for the difference between -273·999948° and -274° is virtually nothing; or it must have a special temperature derived from the collisions of its own atoms, or from the sun. We have said more than once that the temperature of space cannot be so high