of Edinburgh, Session 1882-83. 
223 
1. Bright Clouds on a Dark Night Sky. By the 
Astronomer- Koyal for Scotland. 
2. Mathematical Note. By Mr A H. Anglin. 
3. Note on the Compressibility of Water, Sea- Water, and 
Alcohol, at High Pressures. By Professor Tait. 
The apparatus employed was of a very simple character, similar to 
that which was used last autumn in the “ Triton.” 
It consisted of a narrow and a wide glass tube, forming as it 
were the stem and bulb of a large air thermometer. The stem was 
made of the most uniform tube which could be procured, and was 
very accurately gauged ; and the weight of the content of the bulb 
in mercury was determined. Thus the fraction of the whole con- 
tent, corresponding to that of one millimetre of the tube, was 
found. 
This apparatus had the interior of the narrow tube very carefully 
silvered ; and while the whole, filled with the liquid to be examined, 
was at the temperature of the water in the compression apparatus, 
the open end was inserted into a small vessel containing clean 
mercury. Four instruments of this kind were used, all made of the 
same kind of glass. 
The following are the calculated apparent average changes of 
volume per ton weight of pressure per square inch (ie., about 150 
atmospheres) : — 
Fresh Water, at 12° C. 
Pressure. 
1 
2 
3 
4 
Mean. 
1 
0-00670 
* 
665 
666 
0-00667 
2 
0-00657 
646 
656 
0-00653 
2-5 
0-00651 
650 
640 
648 
0-00647 
3 
0-00641 
633 
636 
636 
0-00636 
Note . — The first two experiments with No. 2 failed in consequence 
of a defect in the silvering. 
The compressibility of the glass was not directly determined. It 
may be taken as approximately 0'000386 per ton weight per square 
inch. 
VOL. XII. 
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