182 Prof. Frankland on the Origin of Muscular Power, 



order in which these salts are mentioned. Plate III. figs. 14, 

 15, and 16 represent the group of bands near E for these salts in 

 the same order, and figs. 18, 19, and 20 the same for the group 

 near F. 



The atomic weight of didymium-chloride is 95*9, and that of 

 the anhydrous acetate 106*9. It will be noticed that all the 

 groups of bands in the case of the salts under examination ap- 

 proach the red end of the spectrum in the order of their increa- 

 sing atomic weights. 



These differences here noticed in the absorption-spectra of dif- 

 ferent didymium- compounds cannot, in our present complete 

 state of ignorance of any general theory for the absorption of 

 light in absorptive media, be connected with other phenomena. 

 They remind one of the slight and gradual alterations in pitch 

 which the notes from a vibrating elastic rod undergo when the 

 rod is weighted, or of the change of tone which an organ-pipe 

 exhibits when the tube is lengthened. 



XXIV. On the Origin of Muscular Power. 

 By E. Frankland, F.R.S* 



UNDER this title there appeared in a recent Number of the 

 Philosophical Magazine an able article by Professors Fick 

 and Wislicenusf, in which these gentlemen describe the results 

 of experiments made upon themselves before, during, and after 

 an ascent of the Faulhorn in Switzerland. In these experiments 

 the amount of measured work performed in the ascent of the 

 mountain was shown to exceed, by more than three-fourths, the 

 amount which it would be theoretically possible to realize from 

 the maximum amount of muscle-oxidation indicated by the total 

 quantity of nitrogen in the urine. 



The data afforded by these experiments appear to me to ren- 

 der utterly untenable the theory that muscular power is derived 

 from muscle-oxidation. Nevertheless, in the application of these 

 data to the problem under consideration, one important link was 

 found to be wanting, viz. the amount of actual energy gene- 

 rated by the oxidation of a given weight of muscle in the human 

 body. Fick and Wislicenus refer to this missing link in the 

 following words : — " The question now arises, what quantity of 

 heat is generated when muscle is burnt to the products in which 

 its constituent elements leave the human body through the 

 lungs and kidneys ? At present, unfortunately, there are not 

 the experimental data required to give an accurate answer to 

 this important question ; for neither the heat of combustion of 

 muscle, nor of the nitrogenous residue of muscle (urea), is known." 



* Communicated by the Author, 

 f Phil. Mag. vol. xxxi. p. 485. 



