46 Chemistry and Physics 



measuring the dispersion of a fragment of plate glass being devised for the purpose. 



Finally, a type of interferometer specially suited for displacement work is constructed. 



Part III records a variety of investigations made at widely different times, but 



in all of which the displacement interferometer was used as a basis of measurement. 



No. 186. BARUS, CARL. Diffusion of Gases through Liquids, and Allied Experi- 

 ments. Octavo, vi+88 pages, 38 figs. Published 1913. Price $1.00. 



In 1900 the author began a series of experiments to determine the rate at which 

 gases diffuse out of a submerged Cartesian diver through water. The method 

 proved to be remarkably sensitive and the results striking. In the present volume 

 the method is perfected, with a view to completing the measurements within a 

 reasonably short interval of time. Diffusions of air, hydrogen, and oxygen into 

 each other, through water and a variety of solutions, are investigated in detail 

 and the diffusion constants determined. It is shown that a method of exploring 

 the internal channels or physical pores of liquids is probably in question. In the 

 course of the work a number of other applications are included ; for instance, the 

 disk of an absolute electrometer is floated on a Cartesian diver submerged in 

 hydrocarbon oil, and the potential is measured absolutely by the pressure needed 

 to just suspend the diver in the liquid. 



No. 229. BARUS, CARL. Experiments with the Displacement Interferometer. 

 Octavo, vi+113 pages, 66 figs. Published 1915. Price $1.00 



This volume contains applications of the displacement interferometer to subjects 

 largely depending on minute angular measurements. Although a location free from 

 tremor and irregular temperature variations could not be found, the development 

 of methods of the kind in question was quite feasible ; and without attempting to 

 push them to a limit, their ranges of application could be fully investigated. 



Among the subjects selected for treatment was the horizontal pendulum. In 

 Chapter I certain available forms of the pendulum, with and without a float, are 

 considered and tested as to their discrepancies, through long lapses of time, by a 

 reflection method. Thereafter the interferometer itself is used, .a method of ap- 

 plication worked out, and the range of application studied through many months. 



In Chapter II an attempt is made to use this interferential horizontal pendulum, 

 for the measurement of the gravitational attraction of two parallel disks. What 

 was obtained, however, was a definite repulsion of the disks, decreasing with their 

 distance apart and appreciable even within 1.5 mm. of this distance. 



Chapter III is introduced as a severe test on the interference equation employed, 

 for the case of path differences resulting when glass columns as much as 10 inches 

 long are inserted in one of the component beams of the displacement interferometer. 



In Chapter IV a number of incidental experiments, on allied subjects, have been 

 grouped together. The possible bearing of certain disk colors of circular gratings, 

 on the somewhat similar phenomenon in coronas, is discussed, as well as the per- 

 formance of the easily available film grating to replace the ruled glass grating, for 

 purposes of displacement interferometry, from a practical standpoint. 



In Chapter V, finally, following the suggestive experiments made in an earlier 

 report, the displacement interferometer is directly applied to the quadrant elec- 

 trometer. The sensitiveness obtained in this way should be of the order of a 

 millionth of a volt per vanishing interference ring. 



No. 249. BARUS, CARL. The Interferometry of Reversed and Non-reversed Spec- 

 tra. Octavo, 158 pages, 99 figures. Published 1916. Price $1.50. 

 In this volume the author has endeavored to generalize the classic experiments 

 in the diffraction of light, by bringing two spectra from the same source to inter- 

 fere under a great variety of conditions. The spectra may be identical and super- 

 posed throughout their extent, or one may be expanded longitudinally, or reversed 

 on a transverse axis, or inverted on a longitudinal axis, relatively to the other. 

 An abundance of new phenomena are thus obtained, some of them useful. The 

 interfering pencils may have any relation to each other, either running in parallel 

 at any distance apart or crossing each other at any angle. Though spectrum inter- 

 ferences are usually obtained, some of them are achromatic. Experiments of this 



