^86 



NA TURE 



[March 26, 1908 



to which Mr. Dines refers by showing that the conditions 

 of the outer atmosphere are isothermal, and Sir James 

 Dewar's experiences with non-conducting power of high 

 vacua ;ire leading to the conclusion that there is a com- 

 paratively warm^interstellar atmosphere. 



C. E. Stkosiever. 

 " Lancefield," West Didsbury, March 3. 



One would naturally expect the upper part of any large 

 mass of fluid to be the warmer, because that condition is 

 a possible one, whereas the converse is not possible as 

 a permanent condition, since it involves a warmer, and 

 therefore in general a lighter, portion of the fluid remain- 

 ing under a heavier. But when dealing with a gas it is 

 necessary to use the term " warmer " in a special sense, 

 for which the convenient expression " potentially warmer " 

 has been used. This means that the temperature is re- 

 ferred to some standard pressure, and taken as what it 

 would be after adiabatic reduction to that pressure. In 

 this sense the air gets rapidly warmer as we ascend, at 

 the rate of about o°-4 C. to each 100 metres, but if there 

 were sufficient mixing we should expect to find the same 

 potential temperature throughout, just as in a pond the 

 heavier water is found at the bottom, but in a fast-running 

 stream the specific gravity and the temperature are the 

 same throughout. 



We have no evidence at the present time to show how 

 the isothermal layer is influenced by a mountain range, 

 but there are immense stretches of sea and land so far 

 removed from any high mountains that we can hardly 

 suppose any such influence to exist over them. 



It must be remembered that the chief heating and cool- 

 ing effects on our atmosphere are applied at the bottom 

 by contact with the ground. Pure air is almost pervious 

 to radiation. There may be sources of heat to the upper 

 layers ; the electric currents which produce the aurora 

 have been suggested, but I do not see that this affords 

 any explanation of the sudden cessation of the temperature 

 gradient. 



The well-known phenomena of shooting stars apparently 

 quite negative the suggestion of a stellar atmosphere ; 

 beside which, unless it were moving with the earth, in 

 which case it would cease to be stellar, such an atmosphere 

 would produce an enormously increased pressure on the 

 forward side of the earth as it pursued its course round 

 the sun. W. H. Dines. 



The Penetrating Radiation. 



In a letter to N.ature of February 13, the question is 

 raised by Mr. W. W. Strong whether the larger propor- 

 tion of the penetrating radiation may not arise from active 

 matter in the air rather than in the ground. Unless the 

 earth's supply of active matter is augmented from without, 

 or unless it arises in a manner at present unknown, the 

 question may be negatived, and a numerical answer given 

 with some approach to accuracy. 



Strutt has found about 3x10-'^ grams of radium as the 

 average amount present in i c.c. of soil. I have found 

 about 10- '° grams of radium to be a measure of the 

 amount of radium emanation present per c.c. of the atmo- 

 sphere (P/ii'L Mag., December, 1907). These two quanti- 

 ties are nearly proportional to the amounts of radium C 

 produced per c.c. in earth and in air. The ratio is 

 30,000 to I. 



But McClelland and Wigger have found that the co- 

 efficients of absorption of the 7 rays are proportional to 

 the densities of the absorbers, so that the absorptions of 

 the 7 rays from radium C by soil and by air are as their 

 densities, about 2000 to i. 



Now it has been proved (P/n7. Mag., September, 1906) 

 that, for a given electroscope near the earth's surface, the 

 penetrating radiations from earth and from air will be 

 in the ratio Q/X to Q'/V, where Q, Q' are the quantities 

 of r.adium per c.c. in soil and air, and X, X' are the co- 

 oflirients of absorption of the 7 rays by soil and air. 



Hence the penetrating radiations from the radium C in 

 the ground and from that in the air are in the ratio of 

 the two ratios above stated, namely, 15 to i. 



Moreover, the radium C in the air is carried earthwards, 

 not only by falling rain, snow, dust, or smoke, but by the 

 pottr'ntial difference in the atmosphere. The active matter 



NO. 2004, VOL. ']']'\ 



on the earth's surface is thus augmented and that in tht 

 air decreased. 



Observers in both hemispheres have found evidence of 

 thorium C in the air, the activity being about half that 

 of the radium C present. The emanation of thorium 

 decays about 6000 times as fast as the emanation of 

 radium, and has a poor chance of escaping from the soil, 

 so that (i) the amount of thorium C in the ground prob- 

 ably exceeds the amount of radium C, and (2) the- 

 thorium C in the ground will be more than fifteen time;- 

 that in the air. 



We may conclude, then, thait at most localities the 

 penetrating radiation due to active matter in the air is less 

 than one-fifteenth of that due to active matter in the earth. 



A. S. Eve. 



McGill University, Montreal, March 3. 



Mosaic Origin of the Atomic Theory. 



The recent correspondence on the subject of the identity 

 of the inventor of the atomic theory has led me to think 

 that the following quotation from one of the foremost 

 English scholars of the seventeenth century is worthy oj 

 some passing notice in this connection. Ralph Cudworth, 

 D.D. (1617-1688), was the author of a colossal monument 

 to Greek philosophy, the " Intellectual System of the 

 Universe." A smaller work of that author, which was 

 published posthumously (1731), contains the following para- 

 graphs, which throw a glimmering light (new, probably, 

 to most eyes) on the historic continuity of ancient philo- 

 sophy and " modern " science : — 



" I. Wherefore we have made it evident, that that very 

 Mechanical or Atoinical Philosophy, that hath been lately 

 restored by Cartesitis and Gassendus, as to the main Sub- 

 stance of it, was not only elder than Epicurus, but also 

 than Plato and Aristotle, nay, than Democritus and 

 Leucippiis also, the commonly reputed Fathers of it. .\nd 

 therefore we have no Reason to discredit the report of 

 Posidoiiius the Stoick, who, as Strabo tells us, affirmed 

 this Atomical Philosophy to have been antienter than the 

 Times of the Trojan War, and first to have been brought 

 into Greece out of Phenicia. If we may believe Posidonius 

 the Stoick, the Doctrine of Atoms is antienter than the 

 Times of the Trojan War, and was first invented and 

 delivcr'd by one Moschus a Sidonian, or rather a 

 Phenician, as Sextus Empiricus cites the Testimony of 

 Posidonius. Democritus and Epicurus invented the Doc- 

 trine of Atoms, unless we make that Physiology to be 

 antienter, and derive it, as Posidonius the Stoick doth, 

 from one Moschus, a Phenician. And since it is certain 

 from what we have shewed, that neither Epicurus nor yet 

 Democritus were the first Inventors of this Physiology, 

 this Testimony of Posidonius the Stoick ought in Reason 

 to be admitted by us. 



"2. Now what can be more probable than that this 

 Moschus the Phenician, that Posidonius speaks of, is the 

 very same Person with that Moschus the Physiologer, that 

 Jamhlichus mentions in the Life of Pythagoras, where he 

 affirms, that Pythagoras living some time at Sidon in 

 Phenicia, conversed with tlie Prophets that were the 

 Successors of Mochus the Physiologer, and was instructed 

 by them. He conversed with the Prophets that were the 

 Successors of Mochus and other Phenician Priests. .And 

 what can be more certain than that both Mochus and 

 Moschus, the Phenician and Philosopher, was no other 

 than Moses the Jewish Lawgiver, as Arccrius rightly 

 guesses. /( seems that it ought to be read Moschus, 

 unless any had rather read it Mochus or Moses. Where- 

 fore according to the .Antient Tradition, Moschus or Moses 

 the Phenician being the First Author of the Atomical 

 Philosophy, it ought to be called neither Epicurean nor 

 Democritical, but Moschical, or Mosaical." 



Dublin, February 26. .Tohn Knott. 



Tabulated Values of Certain Integrals. 

 In reply to the letter of Mr. C. E. Adams in Nature 

 of March 19, a table of the values of the integrals re- 

 quired will be found in Airy's " Undulatory Theory of 

 Optics " (Macmillan and Co., Ltd., 1877) on p. 158. 



Harry M. Elder. 

 41 Netherhall Gardens, N.W., March 20. 



