THERE are Dictionaries and Dictionaries. We have had occasion to expose the shortcomings of some books that are called by this name; it is a far pleasanter task to direct attention to the merits of a work like the one before us, which really deserves its title. Mr. Rodwell's “Dictionary of Science” is a repertory of facts connected with physical science, which will be invaluable to the student. From Chemistry to Chladni's Figures; from Thermo-dynamics to Turacine, scarcely a term will be met with in scientific works, of which the learner will not here find an explanation. The articles have the great advantage of being short, and presenting the salient points of each subject at a glance before the reader's eye; and that their scientific accuracy may be relied on, is guaranteed by such names (amongst others) as those of Mr. Crookes, Prof. Guthrie, and Mr. Wormell in the list of contributors. To illustrate the style of the book, we cannot do better than select two of the shorter articles. The first is on a subject which has recently been discussed in these columns:— A Dictionary of Science: comprising Astronomy, Chemistry, Dynamics, Electricity, Heat, Hydrodynamics, Hydrostatics, Light, Magnetism, Mechanics, Meteorology, Pneumatics, Sound, and Statics. Edited by G. F. Rodwell (London: E. Moxon and Co., 1871.)