1905.] on the Development of Spectro-Chemistry. 135 



in practical life. The need is soon felt of perfecting, and at the same 

 time simplifying, the scientific apparatus. Efforts in this direction 

 have not been wanting in the case of the spectrometer, and they have 

 been crowned with the most brilliant success. 



Professor Abbe, the distinguished physicist who died not long 

 ago, and after him Dr. Pulfrich, constmcted spectrometers on the 

 principle of total reflection. These instruments are distinguished 

 from those formerly in use by their extraordinary simplicity and con- 

 venience, and they allow also of much more rapid work. 



Such instiniments, known as total-reflectometers, have been made 

 for the most exact scientific measurements, and also for medical and 

 technical purposes. Special forms are in use for the examination of 

 fats and oils, milk and butter ; to determine the amount of salt con- 

 tained in salt solutions ; the amount of alcohol and extractive matter 

 in beer ; for the examination of blood and albuminoids in patho- 

 logical fluids, etc. Several of these ingeniously contrived instruments 

 give not only the refractive index and the dispersion of a substance 

 immediately, without any calculation, but also directly the percentage 

 of dissolved matter, e.g. of alcohol and extractives in beer. 



A number of such instruments from the celebrated factory of Carl 

 Zeiss, of Jena, are here exhibited at my request. 



I have now reached the end of my remarks. I have reviewed the 

 development of spectro-chemical research since Newton's time, and 

 we have seen that, although different nations have taken part in the 

 work, a specially large share has fallen to British investigators. For 

 this reason, as I said at the beginning of my discourse, it has been 

 a special pleasure to me to be able to treat of such a subject before 

 the Royal Institution. 



There is a saying of Montesquieu's which I venture to hope has 

 its application to this evening : " Quand vous traitez un sujet, il n'est 

 pas necessaire de I'epuiser, il suffit de faire penser." 



From Newton to our own day — a length of time which our planet 

 takes to complete 250 revolutions round the sun — that is the period 

 through which we have sped in 60 minutes. It will be readily under- 

 stood that on such a rapid trip we have only been able to stop at one 

 or two view-points, and have been obliged to content ourselves with 

 a hasty survey. I chank you all for having ventured yourselves with 

 me on such a hurried excursion, and I shall be happy if it lias been 

 conducted without mishap. 



[J. W. B.] 



