tages; and his great work on logic took a form which could not have been given it if the author had not been a working naturalist as well as a logician. In the second volume of his "System of Logic" Mr. Mill says:
The sanitary question is now uppermost in the public mind, and it is gratifying to see that the discussion of it is not going to be kept as a "mystery" in the medical profession. Every human being is concerned in this matter; and, if sanitary science has any suggestions to make, they must be made directly to the people themselves. This is what the periodical before us aims to do, and this it is doing well. The paper in the August number on the ventilation of the public schools of this city ought to be printed separately and placed in the hands of all the commissioners, trustees, inspectors, superintendents, and other officers connected with the schools not excepting the janitors. The same number contains also the following articles: Cholera stamped out; Animal Refuse of Large Cities; Defective Drainage; Action of Tea on the Human System; Cholera; Morbid Effects of Alcohol; the Public Health; Editor's Table; Book Notices.
Fish-Culture In New Zealand.—Last January a large quantity of salmon-eggs from English waters was shipped to New Zealand. They would reach their destination in 112 days, but it was a question whether they would bear so protracted a journey, though carefully packed and surrounded by ice. To determine this question, four boxes of ova, packed after the same manner as those sent to New Zealand, were deposited at the office of a London ice company. After the lapse of 112 days, these boxes were opened, and the temperature was then found to be 38 Fahr. "In one of the boxes," writes Mr. Buckland, "the eggs nearly all contained living fish; in another they were 'blind,' that is to say, no embryo could be seen in them. In all the boxes there was a certain percentage of eggs which had turned quite white. Some of these white eggs presented a curious appearance—namely, a spot exactly the color of a strawberry, which covered a third of the surface of the egg."
The experiment was on the whole satisfactory, and proves that salmon-eggs may be kept in a healthy condition for 112 days or longer. It is still a question, however, whether the rivers of New Zealand are suited for the cultivation of salmon. Some years ago 1,200 trout ova were shipped to Victoria, and recently Mr. Buckland received from that colony a trout weighing 7 lbs. If salmon thrive equally well in Australasian waters, this essay in "practical natural history" will be productive of immense benefits to the British colonies in the South Pacific at no distant day.
New Theory of Boiler Explosions.—A late number of the American Artisan has a paper by Dr. L. Bradley, on "The Dissociation of Water by Heat as a Cause of Boiler Explosions," in which the author very well shows that such accidents are in many cases produced, not by tension of steam, but by the explosion of oxyhydrogen gas. Dr. Bradley in the first place states very clearly the history of the law of dissociation, or the separation of a compound body into its elements by the force of heat. Under atmospheric pressure the two elements of watery