A year ago last winter, Prof. Guyot deliver-ed a course of lectures in this city, purporting to be at the request of a number of orthodox ministers and others, in which he inculcated the nebular hypothesis, which involves the igneous hypothesis, or central heat of the earth. We took occasion at the time to point out the want of sufficient evidence to make out a case for this hypothesis, and even point-ed out facts which completely nullified it.— During the past winter, Prof. Olmstead of yale College, delivered a course of lectures in ;his city, in which he inculcated the very views we had expressed in this respect, he said " he had differed with his brethren 0i the profession" The nebular hypothesis consists in this, that at one time the whole of the materials of which the bodies of the solar system—sun, planets, and satelites—are composed, were originally in a nebulous state—a thin gas, and that by gravitation and rotation, through a number of ages, planets were consolidated, rings thrown off, and the world formed. This hypothesis is accepted for truth by the majority of astronomers, although it has not a rag to support it. Prof. Olmstead, in speaking of the nebular hypothesis said, " If the nebular theory were true, why should there not be rings existing between the planets. There was a space of nearly one thousand million of miles intervening between Neptune and Uranus; why not then, rings between them, thrown out from the nebulous mass by the centrifugal force, when the entire mass is undergoing process of condensation? Again, it was claimed for this theory that the nearer we approached the sun, the greater became the density of the matter. But that was not true, for Uranus was denser than Jupiter, the earth than Venus, and the sun was only one-half the density of the earth." The nebular hypothesis embraces the " igneous theory," as it is called, namely, that this earth is not yet cooled from its original molten state, that its interior is a hot mass, and that we live on a very thin crust. Hot springs and volcanoes are attributed to this cause, and with a strong degree oi plausibility. David Mushet, however, one of the best practical and scientific mineralogists in* the world, has lately published a letter in the " London Mining Journal," in which he dissents entirely from the views of the Pluto-nists, and overwhelms them with ridicule. He says:— " The uniform cleavage of the fundamental crust In the direction of the magnetic poles was recorded long since by Humboldt, Sedg-wick, and other observers, and suggested to them to hope that such a fact might lead t the discovery of some great natural law.— Now, had this great natural law, when discovered, been compatible with the igneous dreams, could it have been engrafted and bound into the existing volumes of philosophers, it would, no doubt, have been readily received; but, unfortunately, the law of nature annihilated the law of man, therefore, man must continue to teach error, and the law of nature and truth be put to silence.— The inveterate determination to discover volcanic agencies has formerly* as much blinded observation as it now blinds conviction. In Sir Charles Lyell's first edition, where he records with eminent candor and naivete his fruitless diappointment in searching out centres of eruption in Sicily, he relates facts which might have pointed to the truth, but for the engrossing prejudice of ascribing the trifling undulations of the earth's surface to the furious caprice of subterranean fire. He refers to the columnar arrangement of ice in the northern regions of perpetual frost (a striking instance of the magnetic action) without explaining the phenomenon by the fusion or eruption of the ice in the state of lava, as the similar basaltic columns have been theorized to be formed. The masses ol the earth, as much as the crystals that are included in them, are the subject and the product, not of convulsive throes, but of regular definite laws ; and here, as everywhere else, the magnetic or electric fluid is the physical governor of the world." Here we have a strong advocate of the magnetic theory, viz., that the mighty agent which produces and has produced so many changes in our globe, is electricity, and certainly we must say we are surprised that any person of common sense can look upon the face of a granite quarry and believe, (as every Plutonist must) that what he sees there is due to the arrangement of a vitreous mass, while he entertains no such belief respecting a free stone quarry.