210 
Proceedings of the Royal Society of Edinburgh. [Sess. 
XXIII. — On the Application of a Differential Densimeter to the 
Study of some Mediterranean Waters. By John J. Manley, 
M.A., Daubeny Curator, Magdalen College, Oxford. Communicated 
by Sir John Murray, K.C.B. With an Appendix. 
(MS. received June 6, 1907. Read June 24, 1907.) 
From time to time various methods have been employed for the exam- 
ination of samples of sea-water. Of these, the four which have been 
received most favourably by oceanographers are : — 
(1) Estimation of the total combined chlorine per unit volume of water. 
(2) Determination of the relative density. 
(3) Measurement of the refractive index. 
(4) Determination of the specific electric conductivity. 
By any one of these methods it is possible to estimate variations in the 
relative proportions of the saline ingredients of any two samples of sea- 
water. In this paper it is, however, desired to deal chiefly with the prac- 
tical application of the second of the methods enumerated above, to the 
study of some ninety samples of sea- water, collected during the outward 
and homeward bound voyages of the R.M.S. Oruba, under the supervision 
of Mr R. T. Gunther, in the months of July and October 1905. 
Hare’s Apparatus. 
An apparatus which is usually ascribed to Hare, but by Professor A. 
Grey to James Watt, embodies the principle elaborated in the several 
forms of densimeter used in this research. 
Hare’s apparatus may be described as a long-limbed inverted U-tube 
having a short side tube sealed into the uppermost portion of the bend; 
to this side tube a suitable length of rubber tubing, which can be closed 
by means of a pinchcock, is attached ; the open ends of the U-tube dip 
into two glass cisterns. 
To measure the density of a given liquid, one cistern must be charged 
with distilled water, the other with the liquid ; by suction of the rubber 
tube, the liquids are raised to convenient heights within the limbs of the 
apparatus, and the pinchcock is then closed. Finally, the vertical heights, 
