practicable, the centrifugal force of the rotation 

 tends to move the mercury on the stem side of 

 the bubble out toward the bulb, and to hold 

 the mercury on the reservoir side of the bubble 

 tight in the reservoir, inhibiting a separation 

 at the correct breaking point. It is helpful 

 also if the direction of the rotation (clockwise 

 or counterclockwise) is controlled in relation 

 to the direction of flow or movement of the 

 mercury column as it separates. If the direc- 

 tion of movement of the mercury in the pigtail 

 as it separates at the bubble will be clockwise, 

 the rotation of the instrument should be 

 counterclockwise, and vice versa. This will 

 take advantage of any inertia of that part of 

 the mercury which is on the stem side of the 

 bubble, and may assist in inducing separation 

 at the bubble. 



A-13 Appendix. — The Operation oj the Rich- 

 ter and Wiese Reversible Thermometer and the 

 Elimination oj Disturbances (translated from 

 the booklet by Richter and Wiese, Berlin). 



I. Operation 



The visible breaking point makes possible 

 an accurate check of the operation of the 

 thermometers. One is therefore in a position 

 to test the thermometer at any time with 

 regard to its functioning. This is of special 

 importance after the instrument has been 

 transported. 



If the thermometer is in good order, the 

 mercury in the capillary and in the reservoir 

 should not be broken at any point while in an 

 upright position (reservoir down), i. e., the 

 small quantity of air actually present in the 

 capillary must be above the mercury in the 

 bulb of the thermometer. If one now re- 

 verses the thermometer (reservoir up) the mer- 

 cury thread must, if functioning normally, 

 break at the point A (fig. A-2b). If one ex- 

 amines the point A with the help of a mag- 

 nifying glass while reversing the instrument, 

 very slowly, one will see distinctly that the mer- 

 cury commences to run out of the dead arm (fig. 

 A-2a) and then breaks at the point where the 

 dead arm and the capillary meet (fig. A-2b). 

 During this test it is important that the in- 

 strument be as nearly as possible in equilibrium 

 with the temperature of the surrounding 

 medium, in order that the mercury may not 

 rise or fall at the moment of observation and 

 thus render impossible an accurate observation 

 of the breaking procedure. For this reason, 

 the touching by hand of the reservoir during 



the observation should be avoided as much as 

 possible.' 



The quantity of mercury broken off corre- 

 sponds to the actual temperature existing at the 

 moment of breaking. If one turns the instru- 

 ment back again after the breaking (reservoir 

 down), the separated mercury should run out 

 easily from the bulb and should combine with 

 the mercury in the reservoir.^ 



II. Disturbances 



As a result of careless handling during trans- 

 portation or during temperature measurements, 

 or after a long period of storage (in a horizontal 

 position) the mercury may fail to form a con- 

 tinuous thread. 



a. Mercury remaining in the bulb (fig. A-2c) 



In many cases it will be sufficient to reverse 

 the thermometer, a movement which cuases the 

 mercury to run and to combine with the mercury 

 remaining in the bulb. If while again uprighting 

 the thermometer (reservoir down) the mercury 

 runs down as a continuous thread, the instru- 

 ment is in order; but if the mercury continues 

 to break as at first, it is a sure sign that an 

 air bubble is present, perhaps visible with a 

 magnifying glass, which prevents the two por- 

 tions of mercury from being joined. The air 

 bubble must, in that case be forced upwards, 

 above the mercury to the top of the bulb. 

 The following method should be employed: 

 The thermometer is held with the right hand 

 at the bottom of the reservoir; with the instru- 

 ment in a horizontal position, one taps the other 

 end, viz., the bulb, hghtly on the palm of the 

 left hand in order to separate a few globules of 

 mercury which should lie free in the bulb (fig. 

 A-2d). 



Now one reverses the thermometer and allows 

 the mercury to run forward in order to take up 

 the globules; the bulb, however, should not be 

 filled, only the globules should be picked up. 



This manipulation must be repeated several 

 times, while additional globules are being shaken 

 off, until all the mercury will be joined together. 

 The thermometer should not be tapped while 

 in an upright position (with the reservoir down) 

 in such a manner as to allow the separated 

 mercury to run down, because in that case the 

 air bubbles would simply travel downward, let 



' Note diflference between "reservoir" and "bulb." 

 2 It will often be necessary to tap the instrument 

 lightly in an upright position against the under side of 

 a wooden surface, in case the mercury should not thus 

 run easily out of the bulb. 



H. O. 607 



167 



