398 



NA TURE 



[June ,^, looo 



records, dl'd]i during an ascent is normally first negative 

 and later positive. As a mathematician, I recognise, of 

 course, tliat this implies either an absolute discontinuity — 

 a rare event in nature — or else the existence of at least 

 one surface where dt/dh is zero. In the latter event one 

 would naturally expect dtjdh to be small for an appreci- 

 able distance on either side of the surface where it 

 vanishes. 



Coming now to Mr. Gold, if he will refer to my original 

 letter (Nature, March 12, igoS, p. 437) he will see that 

 errors of +10° F. were not asserted to exist as a normal 

 thing, but were suggested as a possible explanation of 

 the following results, which had been quoted by Mr. W. H 



If Mr. Gold can suggest any other explanation likely to 

 carry conviction to those who are sound in the strato- 

 spheric faith, I should be much interested to know what 

 it is. 



The figures quoted by Mr. Gold in his letter show that 

 the examples which I had given of the differences between 

 the teinperatures recorded by two thermometers of different 

 patterns sent up in the same balloon were not exceptional. 

 Unless I misunderstand his figures, they signify that, 

 taking two thermometers of different' types, A and B, the 

 reading from A is the higher when temperature rises and 

 the lower when it falls. Taking both rising and falling 

 readings, the average value of (A ~' B) max. in Mr. Gold's 

 sixteen cases is 3-2° F. In one case it is 63° F. It 

 must also be remembered, as explained in my last letter, 

 that if A— B represents lag, it is likely to be an under- 

 estimate of the true error in the more sluggish thermo- 

 meter. If we take the range of the algebraic difference 

 .\ — B during the ascent and fall, Mr. Gold's figures give 

 a mean of 46° F., the extreme value being 8-3° F. 



The fact that on the average of all the readings, both 

 rising and falling, A — B (or is it A~B?-') is small — on the 

 mean of the sixteen cases almost exactly 1° F. — seems to 

 be regarded by Mr. Gold as a great tribute to the accuracy 

 of the instrument makers. This, however, does not neces- 

 sarily follow, if — as I should naturally assume — the 

 observers followed the procedure customary with meteor- 

 ologists of applying to their readings before publication 

 the corrections obtained by comparing the thermoineters 

 with some recognised standard. This, however, is perhaps 

 hardly germane to the present discussion. 



May 23. C. Chree. 



An Optical Phenomenon. 



I HAVE a greenhouse facing nearly due south. In a 

 vertical pane of glass there is an imperfection. When 

 the sun shines on this pane no light is transmitted through 

 the imperfection. The result is that on a board or piece 

 of paper held at right angles to the sun's rays there is 

 produced an intense black disc about i inch in diameter, 

 the board being held about 8 inches from the glass. This 

 black disc is margined all round by a very narrow, 

 brilliantly white line. 



I can form no explanation of the phenomenon, for, so 

 far as I can see, interference has no chance of acting. 

 The glass is quite transparent, and the flaw so small that 

 I could not find the cause of the black spot for some time. 

 The disc is not hot. 



So far as I can see, the glass is in tension round a 

 central minute imperfection. By " sighting " the pane at 

 v.Trious angles it is possible to detect certain lines. It is 

 difficult, however, to get at them with any accuracy. 

 There is no perceptible difference in thickness. 



I cannot find any reference in any text-book to a pane 

 of clear glass which absolutely intercepts the sun's rays 

 in this way. 



Can anj'one give me an explanation of what appears to 

 be a very unusual phenomenon? V. P. 



Crnhill, Pendennis Road, Streatham, May 22. 



NO. 2066, VOL. 80] 



THE OLDEST REMAINS OF MAN.' 



THE oldest remains of Man with which, until 

 now, we were acquainted date bade to ' the 

 middle Pleistocene, to the Moustier period. They are 

 represented by the cave relics from Neanderthal, Spy, 

 Krapina, Naulette, Malarnaud, and possibly Mentone, 

 by the drift relics from Galley Hill and Bury St. 

 Edmunds. In the memoir under notice, however, we 

 have the description of the two halves of a lower 

 jaw for whicli a much hij.(her antiquity is claimed. 



'sL^'rs.v 



They are attributed to the earliest Pleistocene or 

 even to the late Pliocene. 



The jaw, which, fortunately, contains its comple- 

 ment of teeth, was found 24'io metres below tlie 

 surface in a deposit of sand at Mauer, 10 kilometres 

 south-east of Heidelberg. The date of the discovery 

 was October 21, 1907. 



When found, the two parts were thickly coated 

 by the deposit in which they lay ; the left half had 

 a piece of limestone firmly cemented to it, botli jaw 

 and stone being similarly marked bv dendritic deposits 

 of iron and manganese. The sand in which the jaw 



-Mandibl 



was found is of the same age and nature as the 

 sand of Mosbach, and is attributed to the earliest 

 Pleistocene, although the remains of the fauna found 

 within it justify us to some extent in ascribing' it to 

 an epoch even more remote — the period of the Cromer 

 Forest Bed in England, the late Pliocene of South 

 Europe. The fauna includes, among many species 

 distinctly diluvial. Rhinoceros etruscus, Falc, a horse 



1 " Der Unlerkiefer de^ Homo Heidelbergensis aus den Sanden von 

 Mauer bei Heidelberg." Ein beittag zur Palaontologie des Menschen von 

 Otto Schoetensack. Pp. iv-f 67 ; 13 plates. (Leipzig : W. Engelmann^ 

 1908.) Price 14 marks. 



