Transactions of the Royal Society of Edinburgh . llary tube, e being the uppermost divisionof a small scale, or to some contiguous division. Below e the instrumentdilates considerably, so as to allow of an excess of air being introduced into thehelix by pressure. At / there is a joint of marineglue; and at g, a lateral tube gives access to themercury supply, which can be raised or lowered asdesired, or cut off, or otherwise adjusted, by a clampon the india-rubber tubing through which it h and g were cemented two standard halfmetre scales constructed for me at Kew, and twocorrecte
Transactions of the Royal Society of Edinburgh . llary tube, e being the uppermost divisionof a small scale, or to some contiguous division. Below e the instrumentdilates considerably, so as to allow of an excess of air being introduced into thehelix by pressure. At / there is a joint of marineglue; and at g, a lateral tube gives access to themercury supply, which can be raised or lowered asdesired, or cut off, or otherwise adjusted, by a clampon the india-rubber tubing through which it h and g were cemented two standard halfmetre scales constructed for me at Kew, and twocorrected thermometers; there were thermometersalso at d and c. The bulb of thermometer 2, whichwas the subject of comparison, occupied the centreof figure of the helix ; it was accompanied by a sub-ordinate thermometer for the purpose of calculatingthe exposure correction. The openings of the twopots were closely screened with tin plates duringthe experiments. The readings were made when the principalmercurial thermometer was stationary, or almost so,. Fig. 4. some being taking during an ascending, others during a descending phase; thefive ancillary thermometers and the pressure were read as nearly as possible atthe same time. At every reading the exactness of contact of the mercurywith e was secured by suddenly pinching and relaxing the india-rubber tubing VOL. XXIX. PART II. 7 G 584 MR EDMUND J. MILLSS near to g, and otherwise adjusting the mercury as was necessary. About ten readings on the average were taken to find a mean reading, and from thisa single comparison was deduced. Altogether thirty-three single compari-sons were made. It was considered advisable to employ two glass helices,whose respective capacities were (1) 71*7 cubic centims. and (2) 62-0 cubiccentims. The correction for the barometer was made at Kew; its readingswere reduced by Schumachers tables. The calculations, which were made inaccordance with the well-known formula,* H-/l+^H^-/,1 + ^ VI 1 + at 1 + at [-yKig-
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