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14 reality, the groundwork of his theory. Laboulaye has done no service to the science of Kinematics by this philosophical experiment, for by the apparently convincing form of his proof he has prevented those familiar with the subject from making further investigations. His a priori construction is based entirely upon the motion, of a, and is for that very reason inapplicable to the motions of a, or. In other matters, Laboulaye's book is valuable, and it has without question been the means of widely spreading much useful information; it relies in the practical part confessedly very much upon the infinitely industrious Willis, with whom it sometimes even shares errors.

Morin also, in a little book (1851) intended for elementary instruction, has made a collection of the principles of Kinematics, called, in the later editions,. It is unpretending, and written in a very intelligent manner, and contains some capital leading thoughts, but in essentials it follows Monge's scheme.

In Germany it may almost be said that nothing was done during the period under consideration for the development of theoretical Kinematics. Weisbach, in his article "Abänderung der Bewegung," (Alteration of Motion), in Hülsse's Encyclopaedia (1841), adhered altogether to the system of Lanz,—his own scientific work however had admittedly quite a different direction. Something new might have been expected from Redtenbacher, whose work was so continually connected with mechanisms. His highly philosophic brain perceived strongly the insufficiency of Monge's system; but drawn away from the subject, first in the development of scientific machine construction, and afterwards by his work in mechanical physics, he abandoned it, but did not bring anything new into its place. This was probably his reason for holding that no true system of the study of mechanisms was possible, that they could be arranged only according to their practical usefulness, and for the rest must be treated mathematically. This nihilism may be read between the lines of his valuable work,  (1857), in which he describes and treats theoretically the mechanisms of the collection of models at Karlsruhe. That this book, systemless as it is, has had no inconsiderable circulation, shows that our technical public feel the lively necessity which exists for the theoretical exposition of the subject.