Appendix VI. 



REPORT ON PROFESSOR MORLEYS RESEARCHES. 



Washington, January 17, 1891. 

 Prof. S. P. Langley. 



Dear Sir : The accompauyiug letter from Prof. A. A. Michelson I can gladly in- 

 dorse in every particular. I am familiar with Professor Morley's work, having fol- 

 lowed it from the start, and I know it to be the bfist work of its kind in the history 

 of science. A part of it involves a re-determination of certain physical constants of 

 oxygen and hydrogen ; and on this side of the question the classical researches of 

 Regnanlt are far excelled by the investigations so far made by Morley. Hitherto (for 

 a period of 3 or 4 years), the experiments have been carried on by Professor Morley at 

 bis own personal expense, without aid from any institution. Such a burden no 

 private individual should be compelled to bear ; and I feel sure that aid given by the 

 Smithsonian Institution will redound to its credit, and in the most direct manner tend 

 to fulfill the intention of its founder, himself a chemist. 



The work upon which Professor Morley is engaged is, from a chemical stand-point, 

 fuiulamental in its character, and it has both a theoretical and a practical ])earing. 

 All of the calculations upon which accurate chemical analyses depend rest upon our 

 knowledge of the atomic weights; and the ratio between oxygen and hydrogen is the 

 corner-stone of the entire system. It is both the most important and the mostdiffi- 

 cult to measure of all the atomic weight ratios, and it directly aii'ects nearly every 

 other value in the whole series of constants. Furthermore, all the physical properties 

 of the atoms are now believed to be functions of their mass, and this idea is dominant 

 in the periodic law of Mendelejeff. That law shows the elements to be not independ- 

 ent of each other, but closely related ; so that the exact measurement of their atomic 

 weights bears directly upou the problem of the ultiuiate constitution of matter. If 

 all matter is one entity, then the weights of the different so-called "elementary " 

 atoms should be connected by some definite mathematical law ; and such a law can 

 only bo developed upon the basis of the most refined experimental researches. In 

 the measurement of atomic weights ''accidental errors," which practically vanish 

 from averages, do little harm ; but the " constant errors " are troublesome and all- 

 pervasive. Furthermore, since one atomic weight serves as the starting point for the 

 determination of others, the constant errors become cumulative, and their elimina- 

 tion is anything but easy. 



In Morley's determinations of the atomic weight of oxygen, the errors are controlled 

 by exact manipulation on the one hand, and by wide variations of method on the 

 other. If six or seven distinct methods of measurement, involving dilVerent possibili- 

 ties of error, give at last the same value sought, then the presumption is that constant 

 errors have been eliminated altogether. Up to the present date Professor Morley has 

 investigated the preparation of oxygen and hydrogen in absolute purity, the inlluence 

 of impurities in known anu)unts, the composition of water by volume, and the rela- 

 tive densities of the two gases. The series of exi)erimcnts upon the composition of 

 water by volume have already been made public, and the results obtained are accurate 

 for a single experiment, to within one part in 26,000. Such accuracy was never before 



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