418 Proceedings of Royal Society of Edinburgh. [sess. 
were told they were there, screened from our eyes by 43 millimetres 
of steel. Electric contacts made by mercury on fine platinum wires 
as it rose in the glass tube, forming a long neck to an inverted 
bottle of water, showed, by electric signals outside the gun, the 
volumes of the compressed mercury as measured by the less com- 
pressed glass measure, with the different pressures shown by a proper 
pressure measurer at the times of the electric signals. Tait com- 
municated this novel and ingenious method of measuring an unseen 
liquid by an unseen measuring vessel in a space subjected to a 
pressure of hundreds of atmospheres to Amagat, at a critical time in 
the course of his great work when it was much needed, and proved 
most valuable. In return, Amagat gave Tait the pressure-measuring 
instrument, which was as great an acquisition to him as Tait’s inven- 
tion was to Amagat. 
The Royal Society awards to Professor Tait for this work the 
Gunning Victoria Jubilee Prize. It will, I am sure, be gratifying to 
Dr Gunning, the founder of this prize, that so valuable a contribution 
to science has earned it for the period 1887-90. 
The Keith Prize for 1887-89 was presented to Professor Letts, 
for his Researches into the Organic Compounds of Phosphorus. 
Professor Crum Brown, on presenting the Prize, said : — 
The Council has awarded the Keith Prize, for the biennial period 
1887-1889, to Professor Letts, for his papers on the Organic Com- 
pounds of Phosphorus. The work was difficult, and has been very 
thoroughly done, and the results are of great interest. The special 
difficulty arose from the nature of the substances to be dealt with, 
and also from the want of a trustworthy mode of determining the 
quantity of phosphorus contained in them. The latter difficulty 
Professor Letts has completely got over, and has devised a method 
by means of which the phosphorus in these compounds can be 
accurately determined. The special interest of these investigations 
depends on the remarkable similarities and equally remarkable dis- 
similarities shown by the corresponding compounds of phosphorus, 
nitrogen, and sulphur. It was indeed the desire to trace out these 
analogies and differences through a large series of compounds that 
led Professor Letts to undertake what has turned out to be a very 
laborious piece of work. This steady purpose has given unity to a 
considerable series of papers, in some of which Professor Letts had 
the collaboration of his assistant. Messrs Collie, Wheeler, and Blake 
have thus successively shared in this important investigation. 
