200 Dr. H. R. Wright on the Photometry of the 



Messerschmitt *, and Chwolson f also show great deviations. 

 The results of Wiener J and in one particular case of Seeliger 

 conform in the main to it. Lomirrel J-Seeliger's law 



( simplest form L = T 2 . ds. 



cos i cos e 

 cos z + cos e> 



shows deviations from the results of direct observation which 

 are at least as considerable as are those from Lambert's law. 

 In this connexion, the observations on the radiation of heat are 

 worthy of notice, as they are based on very sensitive objective 

 methods. Provostaye and Desams|l,. Maquenne% Godard ** r 

 and Hutching ft confirm for small angles a of incidence the 

 law of the cosine without any exception. Angstrom |{ alone 

 found empirically Lommel r s law, but this conclusion was due 

 to a fundamental error in the disposition of his experiments, as 

 he himself admits in a later publication. A closer examination 

 o£ the above-mentioned results does not warrant the con- 

 clusions to the extent drawn, by the investigators. They 

 only show that no absolutely matt surfaces are found in 

 nature, and that therefore the law of the cosine is not valid 

 for natural bodies, more particularly in the case of the stars. 

 Seeliger^s experiments were made specially for astronomo- 

 photometric purposes, and it is hence impossible to draw strict 

 deductions from them which shall apply to really matt 

 surfaces. Messerschmitt, on the other hand, committed errors 

 in principle, which will subsequently be referred to ; whilst 

 Kononowitsch used a substance so unsuitable that his results 

 cannot be taken into consideration. It was hence necessary 

 to obtain new T results, which should be based strictly on the 

 grounds which the theory demands. 



* J. B. Messerschmitt, Wied. Ann. xxxiv.. p. 867, 1888. 



t O. Chwolson, Melanges phys. et cliim. tires du Bulk de St. Petersbourg; 

 xii. p. 475-545 und Beibl. xi. p. 149, 1887. 



X Chr. Wiener, Wied. Ann. xlvii. p. 638, 1892. 



§ E. v. Lonmiel, Wied. Ann. x. p. 449 r 1880; Sitzungsber. der math. 

 phys. Classe d. konigl. bayr. Acad, d. Wissensch. zu Munchen, p. 95, 1887; 

 and Wied. Ann. xxxvi. p. 473, 1889. 



|| F. de la Provostaye et P. Desains, Comptes Bendus, xxiv. p. 60 r 

 1847; Pogg. Ann. Ixxiv. p. 147, 1849; Compt Bendus, xxxiii. p. 444, 

 1851 ; Ann. chim. et phys. (3) xxxiv. p. 192, 1852. 



^ Maquenne, Theses presentees a la Faculte des Sciences de Paris, 

 1880. 



** L. Godard, Ann. chim. et phys. (6) x. p. 354, 1887, and Journal 

 de Physique, (2) vii. p. 435, 1888. 



ft C C Hutchins, American Journal of Science, November 1898. 



\\ Knut Angstrom, Wied. Ar,-n. xxvi. p. 253, 1885, and Bihang till k. 

 Svensk. vet. Ak. Handl. xiii. Afd. I. Nr. 4, p. 12, 1887. and Beibl. xiL 

 p. 197, 1888. 



