Pouillet has calculated that if the sun were not supplied with something to make up for the losses he sustains, he must cool at the rate of one degree in a century. But this calculation falls short of the truth. Pouillet supposed that the specific heat of the sun is the greatest which can be conceived. The specific heat of the sun is, it is true, unknown, but instead of placing it at the maximum power, which it is not proved to be, we might suppose it, by an allowable hypothesis, to be equal to that of water, which is well known. Now if we grant to the sun the specific heat of water, we rectify Pouillet's calculation, and we arrive at the conclusion that the sun, if not furnished with any resources from which to repair his losses, would be entirely extinct at the end of 10,000 years. Professor Tyndall, whose experiments are more recent than those of Pouillet, and inspire greater confidence, says: "If the sun were a block of coal, and it were supplied with sufficient oxygen to enable it to burn at the degree of heat proper to that star, it would be entirely consumed at the end of 5000 years." Now the sun has existed for millions of years, for the transition periods of our globe, in which the first living beings were manifested, are traced back to millions of years. And yet his heat has not sensibly diminished since those distant ages. The proof that it has not diminished, is that the climates of the globe at the present time are the same as they were in the tertiary or quaternary epoch. In the tertiary or quaternary strata the same plants and the same animals which exist at present are found. Speaking of times nearer to our own, we may observe that the productions of the soil remain unchanged during the 2000 or 3000 years, whose traditions and historical archives we possess. The sun has lost none of his heat during millions of years. Where has he gotten this heat from? Where does he get it from now? By what means is that unquenched fire kept up. To this question neither astronomy nor physics has ever furnished a satisfactory reply. Treatises, whether astronomical or physical, give us nothing but hypotheses, which we cannot accept. At first it was said that the sun, turning on his axis in twenty-five days, produced by this movement a perpetual friction of his surface against the element in which he moves, in other words, against the ether. But if that were the case, this friction ought to engender a similar heat on the surface of the planets, whose rotatory motion, and especially the motion of translation in their orbit, is much more rapid than that of the sun turning on his axis. Besides, if we calculate the elevation of the temperature which would result from the friction of the sun against the ether, we shall find that the heat would hardly suffice to maintain the radiation of the solar star during one century. This hypothesis is therefore untenable.