1907. | Annwersary Address by Lord Rayleigh. 75 
Laboratory. Among these may be mentioned those by Dr. Harker on the 
Kew Scale of Temperature and its relation to the International Hydrogen 
Scale; Mr. Paterson’s paper, read before the Institution of Electrical 
Engineers—“ Investigations of Flame Standards and the Present Performance 
‘of High-voltage Lamps”; and the eighth report of the Alloys Research 
Committee, by Dr. Carpenter and Mr. Edwards, on the Properties of Alloys 
of Aluminium and Copper. Professor Ayrton, Mr. Mather, and Mr. Smith 
have finished their work on the Ampere Balance, and the paper is now being 
published by the Royal Society in the ‘ Philosophical Transactions, while 
papers on the Silver Voltameter and the Weston Cell are also in the press. 
Dr. Stanton and Mr. Bairstow have completed a further research on the 
measurement of wind pressure, and are well advanced with the investigation 
into methods of impact-testing. 
Other researches in progress are those on the measurement of small 
inductances and capacities, with a view to the standardisation of the wave- 
lengths used in wireless telegraphy, on alloys of copper, aluminium, and 
manganese, for the Alloys Research Committee, and on the properties of 
eutectics. 
The completion of the work on the electrical units will be satisfactory to 
those who have been interested in this question. At the time of my own 
researches about twenty-five years ago, the ohm and the ampere were 
uncertain to 2 or 3 per cent., and I then scarcely hoped to get nearer than 
one part in a thousand. The recent work carried on at Bushey would seem 
to indicate that an accuracy of one part in ten thousand may have been 
attained. The possibility of such a refinement depends largely upon the use 
in the instruments of coils composed of a single layer of wire, the position of 
every turn of which is open to exact determination. The importance of this 
feature was insisted upon by the late Professor Jones. 
Accuracy of measurement appeals less to the lay and scientific public 
than discoveries promising to open up new fields; but though its importance 
at any particular stage may be overrated, it promotes a much needed 
consolidation and security in the scientific edifice. A remarkable example 
of enhanced accuracy is afforded by modern measurements of luminous 
wave-lengths, for which we are mainly indebted to our Copley medallist. 
Not only did he introduce the vacuum: tube charged with mercury or 
cadmium as the best source of homogeneous light, but by a most able use of an 
ingenious method he determined, with the highest precision, the values of the 
cadmium red, green, and blue wave-lengths in terms of one another, and of 
the metre. His work has been skilfully followed up by Fabry and Perot, 
and numerous wave-lengths are now known with a relative accuracy of one- 
