AS A TIMEKEEPER

Evening Post, Volume CXXII, Issue 33, 7 August 1936, Page 17

AS A TIMEKEEPER

IS THE EARTH

FAULTY?

GERMAN CONCLUSION

In an article written some four years ago on the subject of the piezoelectrical properties of quartz crystals —that is, their capacity-to become electrified when compressed or stretched and conversely—brief mention was made of a remarkable application of this effect to the regulation of a new type of clock, first designed and constructed under the.direction of Dr. Marrison, of the Bell -Telephone ResearcWLaboratory in New York, and subsequently, with various modifications, by several of the large national physical laboratories in Europe and America (says a writer, in the Melbourne Age"). ■."■" .' .

Even at that date these crystal clocks had already proved their superlative excellence as timekeepers, though the conclusion of the Americans who had tested 'them—notably, the bankerscientist. Alfred Loomis. of New York —was that, while unsurpassable in accuracy by any other kind of clock over short intervals of time, they were inferior to the Shortt clock—the best of the pendulum type—when time measurements over a-period of weeks or months were in question.

But the claim of the Shortt clock to be the world's best timekeeper, and its hope to outvie the earth itself in this regard, have now been seriously challenged by the results announced concerning the 'performance of the crystal-controlled clocks at the German Reichsanstait (the National Physical Laboratory of Germany). The Reichsanstait has now four of these clocks in operation.. The first of them was put into service in January, 1932; a second in February of the same year; a third during 1933; while a fourth has been employed mainly for experimentation on the effect of various factors on its constancy of rate. It is needless to say that every detail of construction and every circumstance of the conditions of operation which might conduce to erratic or variable performance has been considered with the most scrupulous attention by the men who are engaged in testing these new clocks. Drs. Schneibe and Adelsberger (hereafter referred to as S. and A.). Their detailed reports describing the construction, installation, and performance of these clocks, and the way in which each is checked against the other,'as well as against the wireless time signals from four astronomical time institutes—the, observatories of Greenwich; Paris, Potsdam, and Hamburg—may be read in the "Physikalische Zeitschrift" for November, 1932, and for March, 1936. AX A CONSISTENT RATE Concerning these technical details; it must suffice to say here that the regular vibration of the crystal plate, is employed to maintain the speed of a small electric motor at a perfectly constant rate. : "•' ■•'!.. This motor, suitably geared, constitutes the clock; the comparison of time, as registered by its revolutions, with that shown by other clocks, or wireless signals, is made by recording both on the tape of an electrically operated chronograph. These records show, firstly that the mean daily rate of the crystal clock does not vary by as much as one five-hundredth of a second a day over -a period ;of six months when checked: against : the astronomically determined times from the observatories. (These, -by the way, differ by" a far greater amount from one another.) Secondly, two crystal clocks checked against one another do not vary in their relative rates by more than three ten-thousand-ths of a second a day'; thirdly, that apparent occasional fluctuation in. rate of the crystal clocks with respect to astronomical time are shown simultaneously, arid to a practically equal extent by all the crystal clocks. : In particular, between June 15, 1934, and July 15, 1934, all three crystal clocks showed, as against astronomical time, a change of rate of one two-hundred and fiftieth of a second a day. S. and A. in their latest article, give a very thorough analysis of possible causes of this, change in rate,' and eliminate one by one those which refer the change to any defect in the crystal clocks themselves, or of the. conditions under which they operate. . DUE TO EXTERNAL FACTOR. It is obviously very improbable,- a priori, that three separate vibrating crystals of different 'size arid shape or their associated electrical oscillating circuits, each of which has shown over a period of several months an almost perfect, regularity in the oscillations which govern its motor clock, should suddenly and at the same time develop a change in the rate of vibration of the same amount. S. and A.-are accordingly forced to the conclusion that the change in rate is due to some factor external to the clocks and common to the time-determinations of observatories in England, France, and Germany. Accepting this conclusion; we . are faced with a new and " by-no-means trivial question: Isthis sudden change —which, though very small, is quite definitely proved to occur—in the tirrie at which the stars are observed to cross the meridian—on which observation, of course, the astronomical method of checking clocks depends—due to some common source of error in the method of observation, or does it result from an actual change in the length of a day, that is, of the earth's period of rotation? . S. and A. appear to rule put the former possibility as not worth mention, and give it as their final conclusion that, with the highest probability, this alteraton in rate is to be ascribed, not to the crystal clocks, but to the astronomical time, measurements—that is, to a change in the deputation of the day. • .'■.. I confess that I.find such, a conclusion, even though it concurs^ with deductions- which some astronomers have previously drawn from- apparent . irregularities in the movements of :the moon and planets, ■ very difficult of acceptance. It is hard to conceive of any cause which would- cause the earth thus suddenly to change its rate of rotation without, at;the same time producing movements in the earth's crust, which would have alarming consequences. . ■ . •; REASONS AGAINST IT. For example, if the change were produced by an enlargement of the earth's diameter, the whole crust' '■'■ of the earth would have to rise everywhere by about six inches. The difficulty of accepting this conclusion js apparent when.we consider "that an upward or downward shift of two or three inches only, over a- limited area, is usually associated with a violent earthquake.

Variation due to a bodily shifting of a Continental mass is even less credible, and the melting away of polar icecap in summer, though a "vera causa," seems .hardly likely to be-an adequate one. : /

With all/deference to the view of S. and A., I incline to the opinion .that the cause of this apparent change-in the day's length is more probably, to be sought in some seasonal influence affecting the accuracy of observation of star transits. •