174 
Proceedings of the Royal Society 
fact, the only inorganic solution that I have met with, which when 
mixed with water expands, is ammonium hydrate. "When equal 
volumes of EH 4 HO (sp. gr. -880) and water are mixed, the total 
volume expands *33 per cent. 
Sulphuric and nitric acids show the greatest amount of expansion, 
while hydrochloric acid, when mixed with water, neither expands 
nor contracts. 
Monday , ls£ June 1885. 
EOBEET GEAY, Esq., Vice-President, in the Chair. 
The following Communications were read : — 
c 
1. The Visual, Grating and Glass-Lens, Solar Spectrum, 
as observed in the Year 1884. By C. Piazzi Smyth, 
E.E.S.E., Astronomer-Eoyal for Scotland. 
{Abstract.) 
This paper is the outcome of 12 months’ private spectroscope 
building, two months’ observing therewith, and ten months’ com- 
puting and graphical presenting of the observations. The result is 
a Solar Spectrum map, extending through so many as 60 double 
quarto plates, hut capable of being arranged for the cheapest photo- 
lithographic reproduction, in a manner very easy to examine, con- 
venient for reference, and yet at the same time affording at every 
point new and severe tests for its degree of accuracy. 
This latter important feature has been chiefly obtained by exhibit- 
ing on each plate, vertically one under the other, and on the same 
large, clear scale, five successive and independent series of observa- 
tions of the same Spectrum piece. Two of these several series are 
eclectic collections from the best Solar spectra hitherto published 
elsewhere ; and three , are as many successive and perfectly distinct 
sets of observations by the Author, made during the summer of 
1884 near Winchester. That city being chosen because it was both 
as far South as he could go within the limits of the British country ; 
and be free at the same time from a most serious evil in the atmo- 
