ABSTRACTS OF TECHNICAL ARTICLES 837 



In answer to the first question emphasis is laid on the virtual identity 

 between Laplace's generating function and the Cauchy-Poincaire 

 characteristic function, on the close approach of Laplace's analysis to 

 the form of the Fourier reciprocal equations and to the explicit presen- 

 tation by Laplace of the Ilermite polynomials and related Gram-Char- 

 lier expansion. In answer to the second question, the author submits 

 Laplace's contributions to the probability of causes and points out the 

 distinction drawn by Laplace between the meaning of the word limit 

 when used outside the domain of probability theory and its meaning 

 when the word is attached to the observed frequency with which an 

 event happens. 



As evidence that the Theorie Analytique is in advance of much 

 recent literature, and on account of its great practical value, the La- 

 placian method of dealing with integrands involving factors raised 

 to high powers is outlined. In this connection attention is called to a 

 Laplacian differential equation which contains, as a special case, the 

 differential equation from which Karl Pearson has derived his famous 

 system of frequency curves. 



Method of Enhancing the Sensitiveness of Alkali Metal Photoelectric 

 Cells.^ A. R. Olpin. A technique is described for sensitizing alkali 

 metal photoelectric cells to light by introducing onto the metal surface 

 small amounts of dielectrics, as oxygen, water vapor, sulphur vapor, 

 sulphur dioxide, hydrogen sulphide, air, sodium bisulphite, carbon 

 bisulphide, etc., or some organic compound as methyl alcohol, acetic 

 acid, benzene, nitrobenzene, acetone, etc., or some organic dye as 

 tropaeolin, rosaniline base, eosin, cyanine, kryptocyanine, dicyanine, 

 neocyanine, etc. The marked increase in electron emission from the 

 cathodes of cells so treated is due primarily to an increase in response 

 to red and infrared light. Vacuum sodium cells have been produced, 

 yielding photoelectric currents as high as 7 microamperes per lumen of 

 white light of color temperature 2848° K and caesium cells yielding far 

 greater currents. 



The response of these cells is proportional to the intensity of the 

 exciting light even for light of longer wave-lengths than that to which 

 the cell responded before treatment. 



Spectral response curves are similar for all cells using the same 

 metal as cathode. These curves dilTer from the curves for the pure 

 metal by the appearance of a new selective maximum at lower frequen- 

 cies. This newly appearing maximum resembles the regular maximum 

 for the untreated metal and is due to the presence of the sulphur and 

 air. Changes of approximately 0.8 volt are common. 



^Phys. Rev., July 15, 1930. 



