144 Instructions for Making and Registering 



the junction of the bulb and tube ; then, by cautiously hea/mg and cooling 

 alternately the bulb, the tube, or the air vessel at the top, as the case may 

 require, the disunited parts of the spirit may be distilled from place to place, 

 till the whole is collected in one column in union with the spirit in the bulb. 



2rf, The Mercurial Thermometer. When the steel index gets immersed 

 in the mercury, it cannot be moved by a magnet, and lets the mercury pass 

 by its side. First cool the bulb (by evaporation of ether, if necessary) till 

 the mercury is either fairly drawn down below the index, or a separation 

 takes place in the column, leaving the index with mercury above it. Endea- 

 vour then, by tapping, warming the tube, or by the magnet, to loosen the in- 

 dex ever so little, then apply heat to the bulb, and drive up the index with 

 its superabundant mercury quite into the air-vessel. This requires many 

 trials and much patience. When there, hold the instrument bulb downwards, 

 and suspend the index by a magnet at the top, allowing any globule of mer- 

 cury to drop into the origin of the tube below ; then heat the bulb cautiously 

 over a very small clear flame of an oil lamp, till the mercury rises to the very 

 top of the tube, and fairly unites with the globule there awaiting it. Let the 

 bulb cool, and the mercury will sink in one united column ; if not, heat it 

 again. When this is accomplished, the index may be set loose, by withdraw- 

 ing the magnet, and restored to its proper position in the tube. 



A self-registering thermometer may be advantageously left (properly se- 

 cured) for a whole year, or parts of a year, on elevated summits or other re- 

 markable points, to ascertain their maxima and minima of temperature du- 

 ring absence. In such cases, take care to defend them from discovery, or 

 acc! ^mt from wild animals, birds, snakes, &c. In taking it up for reading 

 off, observe not to derange the indexes, and do not leave it without seeing 

 that the indexes are in contact, and the temperature that of the air at the 

 moment. 



Of Thermometers buried in the Earth. — Thermometers buried at different 

 depths, for the purpose of examining the monthly changes of temperature of 

 the soil, should have their balls and lower part of the scale well wrapped up 

 in woollen cloth or pounded charcoal, and should be placed in strong earthen 

 vessels, which may be entirely withdrawn from the ground so as to allow of 

 inspecting and reading off the scale, without exposing the balls to any possi- 

 bility of changing their temperatures while under examination. The vessels 

 should be fitted with covers, to defend the scale from injury in burying and 

 digging up. 



A pipe of earthenware (composed of separate pieces), or one of wood, may 

 be sunk ten or fifteen feet below the surface, into dry earth, and a thermo- 

 meter, defended as above, lowered by a chain. The pipe being then ob- 

 structed at every two feet by some stuffing readily hooked up, the thermo- 

 meter may be easily examined, and a register of its indications kept with 

 very little trouble. In like manner, the temperature of wells may be regis- 

 tered. 



0/the Temperature of the Sea The surface temperature of the water at sea 



should be registered, as a matter of course, with the same regularity and at 

 the same hours as the barometer and thermometer. It is more conveniently 

 (and with quite accuracy enough for the purpose) obtained by taking up a 



