1876.] Rev. S. Haugliton on the Law of Fatigue. 131 



to the power of air to disseminate crystals of a salt thrown into it \\\ 

 fine powder. 



De Coppet has already remarked that the mass of a solution exerts 

 some influence on its crystallization, and I have shown that the form of 

 the vessel also has a decided effect. The effect again of different vibra- 

 tions on different solutions is worth trying, as there seems to be no 

 reason why the hyperacid sodium salt should be an exceptional case. 

 . A good deal of work has yet to be done before we arrive at a satis- 

 factory explanation of these obscure phenomena. 



IX. ''On some Elementary Principles in Animal Mechanics. — No. 

 VIII. The Law of Fatigue.^^ By the Rev. Samuel Haugh- 

 TON, M.D. (Dubl.), D.C.L. (Oxon.), F.RS., Fellow of Trinity 

 College, Dublin. 



In my last paper (No. VII.) I illustrated the Law of Fatigue by experi- 

 ments made in lifting weights varying in amount, wdthout rest, at a fixed 

 rate of motion ; I shall now illustrate the Law by experiments made in 

 lifting a fixed weight at var3dng rates of motion, without rest, as before. 



Law of Fatigue. 



" When the same onuscle (or group of muscles) is kept in constant action 

 until fatigue sets in, the total work done multiplied by the rate of work is 

 constant.''^ 



The following experiments were made during the last six months by 

 Dr. Macalister and myself : — 



A pair of 10-lb. dumbbells, held one in each hand, were raised simul- 

 taneously from the vertical to the horizontal position, and again lowered, 

 at a rate regulated by a metronome made for the purpose. No rest was 

 allowed at the beginning or end of the motion, which took place as 

 before, under the following conditions, viz. : — 



1. To keep time with the metronome. 



2. To raise the weights in the transverse plane. 



3. To supinate the hands. 



4. To abstain from all bending of the knees or spinal column. 



5. The experimenter not to count the lifts. 



The experiments were made at intervals never less than 24 hours, so 

 as to avoid all risk of the muscles becoming trained ; and on each occa- 

 sion the weights were lifted until it became impossible to effect another 

 hft, without violating condition No. 4, indicating that other muscles 

 were called in, to aid the shoulder-muscles already worn out. The fol- 

 lowing results were obtained, the exact weight of each dumbbell being 

 9-75 lbs. 



