Effect of Pressure upon the Spectrum of an Element. 119 



by any but a professional glass-blower ; the first form, on 

 the other hand, can easily be put together by anyone who 

 can do the most rudimentary glass-blowing. 



In order that the indiarubber cork may form a thoroughly 

 air-tight joint, it must be well cleaned with benzene, coated 

 with indiarubber solution, and put in place while the solution 

 is wet. When the solution has got thoroughly dry, which 

 takes four or five days, the joint will be quite air-tight. 



"With such an arrangement the thermometers can easily be 

 maintained at a temperature constant to within 0°' 01 for three or 

 four hours together. The manometer is only used to adjust the 

 temperature to the desired point, a table of vapour-pressures 

 being employed. In about half an hour after altering the 

 pressure, and hence the temperature, the thermometer 

 readings become quite constant. The instrument once started 

 can be left entirely to itself ; the only thing the observer has 

 to do is to read the thermometers, then let a little more air 

 in to get the next higher temperature. He may then go 

 away for half an hour, and when he returns will find the 

 temperature constant and can take the new readings. 



XVI. Note on the Effect of Pressure upon the Series in the 

 Spectrum of an Element. By J. S. Ames and W. J. 

 Humphreys*. 



IT has been known for many years that the spectra of certain 

 elements, notably the alkalies and the alkaline earths, 

 contained series of lines, which obeyed a mathematical law 

 like that giving the distribution of lines in the spectrum of 

 hydrogen. These series have been thoroughly studied by 

 Kayser and Runge, who have classified them according to 

 their physical characteristics as principal, first subordinate, 

 second subordinate. Only a few elements, lithium, sodium, 

 potassium, have in their spectra all three series ; while the 

 last two series, the subordinate ones so-called, are common to 

 some ten others ; the wave-lengths being different in the 

 spectra of the different elements, the physical properties being 

 the same. 



While the shift of the lines in the spectra of the elements 

 was under investigation, it seemed important to study in par- 

 ticular the effect of pressure upon the series of the various 

 elements. To this end, photographs were taken of the arc- 

 spectra of all elements which give series, both at ordinary 

 pressure and at increased pressure ; and the shifts were care- 

 * From the Johns Hopkins University Circulars, June 1897. 



