1888.] Reflexion and Transmission of Light ly Glass. 101 



Superficial mamibrial : clavicular and anterior part of pectoralis 



major, sometimes separate from the remainder of the 



muscle. 

 Deep mamibrial: occasionally present as the pectoralis minimus 



of Wenzel Gruber. 



Gladiolar : posterior, non-reflected part of pectoralis major. 

 Costal : double (1) pectoralis minor, (2) deep reflected part of 



pectoralis major. 

 Abdominal : occasionally present as pectoralis quartus, or as 



some of the forms of achselbogen. 



III. "Some Observations on the Amount of Light reflected and 

 transmitted by certain kinds of Glass." By Sir JOHN 

 CONROY, Bart., M.A., Bedford Lecturer of Balliol College 

 and Millard Lecturer of Trinity College, Oxford. Com- 

 municated by A. G. VERNON HARCOURT, Esq., F.R.S. 

 Received November 8, 1888. 



(Abstract.) 



The experiments were commenced in order to determine the amount 

 of light lost by transmission through glass. 



Plates of the same kind of glass, but of different thickness, were 

 taken, and the amount of light they transmitted determined, and 

 from these values the percentage amounts reflected and obstructed 

 calculated. 



The amount reflected from the first surface was also determined 

 directly by measuring the relative intensities of the illumination pro- 

 duced by two argand flames, when the light from both fell directly on 

 the photometric surfaces, and when the light from one fell directly 

 whilst that from the other reached the photometer after reflection 

 from the surface of the glass. 



Experiments were also made to ascertain whether repolishing 

 altered in any way the reflective power of the glass ; and the 

 polarising angles of the glass before and after repolishing were also 

 determined. 



Conclusions. 



It seems probable that the amount of light reflected by freshly 

 polished glass varies with the way in which it has been polished, and 

 that, if a perfect surface could be obtained without altering the 

 refractive index of the surface-layer, then the amount would be 

 accurately given by Fresnel's formula, but that usually the amount 

 differs from that given by the formula, being sometimes greater and 

 sometimes less. 



H 2 



