It is humiliating to behold men somewhat distinguished and devoted to the teaching of science as a profession, arraying the vagaries of their minds in the garb of science, and thrusting them upon the public under the assumption of "profound deductions," and yet this is by no means uncommon. Such attempts appear to us, like Buncombe speeches, got up for the purpose of astonishing those who do not know the difference between sense, sound, or science. At the meeting of the Association for the Advancement of Science, held last week in Baltimore, Professor Alexander read a paper on the "numerical harmony of the solar system," but to render the theory perfect, some planets were missing. Nothing daunted in supplying such an omission, the periodic comets were brought in to supply the place of the missing stars. But how many comets, we ask, would be required to supply the place of a missing planet the size and density of the earth? Practical science can answer this question. It would take no less than 466,561,074,-074,074,074—over four hundred and sixty-six thousand billions—each one hundred and eighty miles long. If there were such a number of comets in our solar system, we would see them darting through the heavens nightly, as thick as fire flies in July evenings. To find such a number of comets, we suggest to our harmonious philosophers the showers of stars which annually take place in August. They will find them very convenient to supply the deficiency. In a lecture on comets, delivered by Professor Nichol, last winter, in the Glasgow Athenseum, he said, " What is a comet ? A simple handfull of mist ? no, that was too thick for a comet. The large comet seen in 1842, which was so long that if its head were at one end of the earth's orbit, its tail would come out of the other—180 millions of miles —was so light, that if it could be squeezed together to the density of water, the lecture room of the Athenseum could easily contain it. That was no theory, but positive fact, clearly proved." Upon this data, considering the lecture room named to be 150 by 100 feet, and 30 feet high in the ceiling, we have made the calculation above, thus showing that the prodigious number of four hundred and sixty-six thousand billions of immense comets, would be required to supply the place of one planet like our compact and venerable mother Earth. Having presented these figures, and described the attenuated structure of these " wanderers of the skies," we hope none of our readers will, after this, be afraid of comet collisions. It should be the object of teachers of science to present their views on all subjects with great caution, and to theorize but little. Their duty is to present facts and describe experiments, not hypotheses and vagaries. It is no doubt very safe for some philosophers to indulge in scientific speculations, which never can be brought to the test so as to risk their reputation, but this neither advances science nor confers lasting honor upon themselves. They may gain a transitory distinction and an ephemeral adulation from some persons, by the very oddity of their views, but that is a miserable reward for time misspent and intellect frittered away upon the most useless subjects—mere vagaries.