May g, 1878] 



NATURE 



41 



apparent paradoxes 

 instructive. 

 May 7 



At the 



same time it cannot fail to be 

 Latimer Clark 



Cumulative Temperature 



Attention has been called in your valuable paper to the 

 idea of registering cumulative temperatures by means of a pen- 

 dulum, by M. von Sterneck, vol. xvii. p. 308, and this has 

 called forth several letters. One gentleman has put forward 

 my name as having devised means with some success. In 

 an instrument exhibited at the Royal Society soirk, 1876, 

 I could have left the matter resting at this point, but I am 

 induced to write by the letter of your correspondent, "B,"in 

 vol. xvii. p. 486, who says, " The chief merit in this matter 

 will belong to the person who puts the idea into a working form 

 which can be proved capable of giving acciurate results." As I 

 think that I have fairly attained this end, or at least pointed out 

 the way to it, with your permission I will describe the means 

 which appears by the correspondence interesting to many of 

 your readers. In my cumulative temperature clock the impor- 

 tant element, fhe pendulu?n, is constructed as follows: — A steel 

 cylindrical tube 32 inches long, if inch internal diameter, is 

 hermetically closed at both ends. A rod is attached to one of 

 the ends, which is placed uppermost, to connect this pen- 

 dulum with the clockwork in the ordinary manner. An air- 

 tight division is made across the tube or chamber at 5 inches 

 from the upper end. A small tube leads from this divi- 

 sion to the bottom of the chamber. A conical plug is in- 

 serted in the upper chamber, to be hereafter described. A 

 screw plug is placed under the small tube in the outer tube to 

 enable the upper chamber to be filled with mercury. When the 

 pendulum is so constructed, the lower screw plug is removed, 

 and the upper chamber and leading tube filled with mercury by 

 means of a small funnel. In this full state the mercury is boiled, 

 and the whole inverted. It then becomes a steel barometer. To 

 convert it into a thermometer, a small air-hole is made in the 

 outer tube (this is not shown in the engraving), and this hole is 

 closed up with a small air-tight cock filled with a porous mate- 

 rial. When this is screwed on and turned off, it is isolated from 

 atmospheric pressure, and the mercury rises into the upper 

 chamber by any increase of temperature causing expansion of 

 air in the tube, and sinks in the same manner by loss of tem- 

 perature, so that the pendulum becomes simply an air thermo- 

 meter. The pressure of the air by expansion within the tube 

 in the rising of the mercury changes the centre of oscillation of 

 the pendulum and accelerates the clock, and vice versd. 



The clock is specially constructed to count beats only in units, 

 tens, &c., up to ten millions, and the number of beats per day, 

 week, month, or year, becomes the unit of temperature for the 

 period. The exact length of time of each pendular oscillation 

 being governed by the temperature at the time, the method 

 becomes equal to one accurate observation at every second of 

 time. 



The difficulties of construction and refinement required upon 

 this general description are of two kinds, mathematical and 

 mechanical. The models that I exhibited at the Royal Society's 

 soiree were imperfect, being of blown glass. The difference of 

 oscillation per day for 1° Fahrenheit, was in these about 50, as 

 taken at the Lambeth Observatory by the late Col. Strange. 

 In the steel instruments described there would be about 100 

 oscillations additional per day for the rise of each degree centi- 

 grade. The mechanical difficulties are simply constructive. To 

 obtain perfectly vacuum proof chambers, and to follow correctly 

 the outline of the plug to be immersed in the vacuum- 

 chamber. Also the adjustment of the correct volume of mercury, 

 and the density of the contained air, by means of the cock, and 

 the application of heat or cold to the outer case. The mathe- 

 matical requirements are corrections. Thus : if the chambers 

 were simply cylindrical, the mercury that rose by the pressure 

 would have a different oscillation value for every point of space 

 through which it rose. This might be corrected to equal scale 

 value by making one or both the mercury-chambers conical, but 

 it is much more simply done by inserting a conical plug in the 

 upper chamber. There would also be a correction for the ex- 

 pansion of the mercury and the steel case, and from any iiTa- 

 tionality in the expansion of the contained air. The whole of 

 this correction being derived from heat might he. made by one 

 correction in the immersed plug. Prof .■ Stokes, Sec. R.S., 

 kindly offered to calculate the exact form of this plug for me 



from data I was to supply. But I was ill shortly after this, and 

 unable to attend to the matter, so I let it drop, but have the 

 clocks and pendulums ready to complete some time hence. 



I send a diagram engraving which shows the principle of the 

 pendulum No. 2, for cumulative temperatures. No. i is for 



^jpsa Ei^^ 



y 



taking cmnulative pressures upon the same system, if the 

 science of meteorology should require such exact means 

 of obtaining permanent records of pressure and temperature for 

 long periods as for months or years. Wm. F. Stanley 



South Norwood, April 22 



THE INTERIOR OF THE EARTH ^ 



SIR GEORGE AIRY remarked that the nature 

 of the subject was dififerent from any upon 

 which he ever lectured before, in regard to its inde- 

 finiteness and to the difficulty he should have if he 

 considered it to be his duty to lead them definitely up to 

 some point. He could only give them some idea ,^f the 

 theory to which he wished to lead them, and in doing so 

 he would advert collaterally to a good many points which 

 might be valuable. He proposed to divide his address 

 into three parts. The first would relate to the measures 

 of the earth ; the second to observations on temperatvire ; 

 and the third to the manner in which they might suppose 

 the earth to have been formed, especially with regard \.o 

 the nebular hypothesis ; and after that he would add 

 some remarks on the conclusions to which these lead. 



He described the process called triangulation, by which 

 a large part of the contour of the globe is covered, 

 and by which it is possible to lay do-wn a map on which 

 the distance between any one point and any other point 

 is ascertained to within a few inches ; how that this was 

 valuable in ascertaining the dimensions and figure of the' 

 earth with the aid of the zenith sector, an instrument 

 for measuring the apparent distances of stars from the 

 point overhead. He showed on a large globe the prin- 

 cipal lines of measurement which had up to this time 



' Abstract of Address at the Cumberland Association for the Advance- 

 ment of Literature and Science, by Sir George B Airy, K.C.B., F.R.S., 

 As'tror.omer-Royal. Revised by the author. 



