PHYSICS. <)1.'> 



suits obtiiiiied by Mascait and Esselbach with quartz in the ultra violet, 

 and by Mouton and Langley for flint in the ultra red, and linds the for- 

 mula very exactly verified in all cases. In the case of quartz the discrep- 

 ancy reachCvS the third decimal place of the index only for the, extreme 

 red (A =21-4 x 10-^) In the case of flint the divergence becomes 

 sensiible only for the line O and for the extreme red (A = 28 x lO"'*). 

 For the line O the value observed, 1-C266, lies between 1-6242 and l-()277, 

 calculated from Mascart's and Esselbach's wave lengths. ( Wied. Ann.^ 

 XXIII, 306 ; J. Phys., July, 1885," II, iv, 324.) 



Clemenshaw exhibited to the London Physical Society some experi- 

 ments in projecting the spectra of the metals without the aid of the 

 electric light. A small quantity of a solution of the salt to be experi- 

 mented on is put into a bottle in which hydrogen is being evolved by 

 the action of dilute sulphuric acid on zinc. The bottle has three necks, 

 through one of which an acid funnel is passed, a second carries the jet, 

 and through the third hydrogen or coal gas is fed into the apparatus, the 

 flame being thus regulated. The jet, which is from one-eighth to three- 

 sixteenth inch in diameter, is surrounded by a larger tube, through 

 which oxygen passes to the flame ; the result being a brilliant light 

 giving the spectrum of the substance, which is carried over mechanic- 

 ally by the evolved hydrogen. The spectra of sodium, lithium, and 

 strontium were shown upon the screen and the absorption of the so- 

 dium light by a Bunseu flame containing sodium was clearly seen. [Phil. 

 Mag., May, 1885, V, xix, 365 ; Nature, February, 1885, xxxi, 329.) 



Koenig presented in May to the Physical Society of Berlin the plan 

 of a new spectrophotometer then in course of construction. It consisted 

 of a tube containing a lens and a diaphragm turned toward the source 

 of light, and having two slits lying the one above the other, a i^rism for 

 decomposing the two incident beams, and a second collimating tube 

 with a disk closing the end, on which appeared the two spectra slightly 

 separated. Before the lens of the observing telescope was placed a twin 

 prism, the two halves, with refracting edges of 1° to 2°, being cemented 

 together. By this twin prism each spectrum was decomposed into two 

 spectra, and the dimensions of the twin i^rism were so determined that 

 on the disk of the collimator one spectrum was situated above the other 

 below, while in the middle the second spectrum from the upper slit 

 coincided with the second spectrum of the lower slit. In the disk of the 

 observing telescope a small opening is made cutting ott' a small piece 

 of determinate wave length from the double spectrum, so that on look- 

 ing through it the field of vision is seen divided by a line (the refract- 

 ing edges of the twin prism) into two halves, both of the same coloring. 

 Before each of the two slits of the slit collimator a Nicol prism was placed 

 in such a position that light polarized in a vertical plane entered one 

 and in a horizontal plane the other. The middle compound spectrum 

 consisted therefore of a vertically and a horizontally polarized spectrum, 

 and in the field of view the two like-colored halves were also polarized 



