Page:Popular Science Monthly Volume 49.djvu/729

Rh length. This discussion contains much interesting matter bearing upon the history of glacial theory, the subject at the time Tyndall wrote being in heated controversy. In order that the pages now reproduced might contain nothing touching the views of others which Prof. Tyndall might have wished at the present time to alter or omit, his widow submitted the historical parts to Lord Kelvin, who assures her that, in his opinion, "the statements on controversial points in this beautiful and interesting book of your husband's are all thoroughly courteous and considerate of feelings, and have been felt to be so by those whose views were contested or criticised in them." The beginning of Tyndall's study of glaciers proceeded from a discourse on slaty cleavage which he delivered at the Royal Institution, in June, 1856. This discourse is appended to the volume. Some sixty simple illustrations aid in making clear the text.

Dr. H. Holbrook Curtis's work on Voice Building and Tone Placing relates to the singing voice. The author has invented a method of tone exercises for overcoming serious affections of the vocal cords which has been used satisfactorily by the most renowned singers, and he furnishes here an exposition of the physiological principles, and the elementary laws of sound and music, on which it is based. The chapters on anatomy and respiration are intended to be of value to the physician as well as to the student of singing; and for that reason also the subject of the vibration of the vocal cords has been considered in a way in which it is not entered into in any other work. The author's theory that the overtones introduced by the proper method of placing tones in the facial resonators induce a new plan of vibration of the vocal cords has recently been verified by the investigations of Prof. Oertel, of Munich, and several of his experiments have been introduced to explain the true plan of vibration of the cords as seen in the stroboscope. The author has also tried, with the aid of these experiments, to elucidate his theory as to the removal of "singers' nodules" by tone exercises in a scientific way. The general scheme of the building of the voice, in accordance with the author's theory of tone placing, is appended for the benefit of teachers and students. The book is the result of a vast experience with singers. The ideas have been put together in a concise and simple way, without any attempt at elaboration of style. The closing chapter, on Voice Figures, in which the vibrations are translated into pictures of great variety and beauty, has more than a physiological or acoustic interest. It is a revelation of the grace and æsthetic charm with which Nature's processes are found to be invested, whenever we are able to recognize them.

In his discussion of the Primary Factors of Organic Evolution Prof. Cope attempts to select from the mass of facts accumulated by biologists those which, in his opinion, throw a clear light on the problem of organic evolution. As the actual lines of descent can be finally demonstrated chiefly from paleontological research, a large part of his evidence is drawn from that source. Another reason for preferring the paleontological evidence is that Darwin and his school have drawn their evidence from œcology and Weismann and writers of his type from embryology, leaving the paleontological field less worked. The mass of facts recently brought to light in the field of paleontology, especially in the United States, remained to be presented, and the evidence they contain to be interwoven with that derived from the sources mentioned. The view is accepted, to which many zoölogists are now inclined, that the factors of evolution which were first clearly formulated by Lamarck are really such; and the research has proceeded on the assumption that every variation in the characteristics of organic beings, however slight, has a direct efficient cause. Any theory of evolution which omits the explanation of the causes of variations, Prof. Cope holds, is faulty at the basis. Hence the theory of selection can not answer the question asked, although it embraces an important factor in evolution. The subject is considered under the several headings of