Jan. 23, 1890] 



NA TURE 



271 



" Some light has been recently thrown on the illness of 

 Newton by Dr. Dowson, of Whitby, who, at a meeting of the 

 Philosophical Society there on the 3rd of January, 1856, read a 

 paper 'On the Supposed Insanity of Sir Isaac Newton,' in 

 which he has shown that the malady with which he was afflicted 

 in September 1693 was probably influenza or epidemic catarrhal 

 fever, which prevailed in England, Ireland, France, Holland, 

 and Flanders in the four last months of 1693. This distemper, 

 which lasted from eight or ten days to a month, was so general, 

 that ' few or none escaped from it ' ; and it is therefore probable, as 

 Dr. Dowson believes, that Newton's mental disorder was merely 

 the delirium which frequently accompanies a severe attack of 

 influenza. See Dr. Theophilus Thomson's ' Annals of Influenza 

 or Epidemic Catarrh in Great Britain,' published in 1852 by 

 the Sydenham Society. See also the Philosophical Transactions 

 for 1694, vol. xviii. pp. 105-115." W. Greatheed. 



About forty-five years ago I paid a visit with a friend to the 

 laboratory of the celebrated chemist Prof. Schonbein, the dis- 

 coverer of ozone in the atmosphere and the cause of influenza. 

 Just prior to our visit the Professor had obtained some ozone, 

 and had inhaled it for the purpose, as he said, of giving himself 

 influenza, in order to ascertain how it would affect him. We 

 both distinctly observed most of the ordinary symptoms of the 

 malady. Augustus Harvey, 



12 Landridge Road, Fulham, January 17. 



Rainbow due to Sunlight reflected from the Sea. 



I HAVE never heard of a rainbow, due to the image of the sun 

 in water, having been seen ; and I think the following letter, 

 from an old student of mine of sixteen years ago, may interest 

 your readers. WiLLIAM THOMSON. 



The University, Glasgow, January 7. 



On September 18, 1889, I saw a rainbow, caused, not by the 

 direct rays of the sun, but by their reflection from the sea. 



We were at the height of 900 feet ; the sky was all clouded 

 except along the western horizon ; the sun, an hour before set- 

 ting, was hidden ; but its rays were reflected from the sea. A 

 drizzle was falling, and my companion was remarking how strong 

 the light from the sea was, when it occurred to me that it might 

 give a bow. And there it was behind us — not the usual recum- 

 bent bow, less than a semicircle, but an overhanging one, greater 

 than a semicircle. The clouds were drifting from the west, so 

 that the sun came into view ; and the usual rainbow became 

 visible with its secondary bow ; so that three rainbows were seen 

 at once. The sea-bow and the usual bow were identical at the 

 horizon. The angle between them was greater than the sun's 



angular height, but not double. It seemed as if the complemen- 

 tary segment of the rim had been folded up from beneath into 

 view, but that the colours were not reversed. The sea-bow was 

 just as bright as the secondary bow, which it intersected. 



From the fact that the three were seen together, for over 3 

 minutes, at least in part, I would argue that it is no unusual 

 sight, and that in Scotland, where bows are so frequent, and 

 plenty of comparatively smooth water available, this sea-bow 

 may be looked for and seen. 



I may mention, also, that I saw a fourth bow that evening. 

 After the sun had set, a bow of one colour, an orange-pink, took 

 the place of the usual bow. The source of light, I thought, was 

 a cloud just over the place where the sun had set. 



William Scouller, 



86 Calle de la Independencia, Valpiaraiso, November 9, 1889, 



Osteolepidae, 



Your reviewer R, L. is mistaken in condemning so absolutely 

 the above form. The word " Osteolepus " would be a legitimate 

 adjective expressing the same idea as the substantive Osteolepis ; 

 and the patronymic of the "Osteolepi" would be simply 

 " Osteolepidae," and not " Osteolepididse." 



It may be useful for R. L. and some others to apprehend this 

 principle in word-building — viz, that compound Greek adjectives 

 do not take the lengthened genitive as root ; thus the correct 

 Latin equivalent for the corresponding Greek adjective is not 

 " echinodermatus " but "echinodermus," not "distomatus" 

 but " distomus," Hence, the correct form for the neuter plural 

 of the former is " Echinoderma ; " and for the neuter singular of 

 the latter is Distomum, And it would be wrong to write " Dis- 

 tomatidse" as the family name, and correct to write " Disto- 

 midse." Hence Osteolepidae and the like are admissible, since 

 they may be considered as formed from adjectives, and not from 

 the substantive (of questionable form itself) in -is. 



R. L. -f E. 



Exact Thermometry. 



Since the publication of my letter in Nature (December 19, 

 1889, p. 152) on the cause of the rise of the zero-point of a ther- 

 mometer when exposed for a considerable time to a high 

 temperature, two letters on the same subject have appeared, one 

 from Mr. Herbert Tomlinson (January 2, p. 198), the other from 

 Prof. E. J. Mills (January 9, p. 227), who replies to my 

 objections to the plastic theory. 



Mr. Tomlinson considers that my experiments seem to leave 

 no doubt that compression, due to the plasticity of the glass, is not 

 the main cause of the rise of the zero-point, but he considers that 

 it is not merely the prolonged heating, but also the change of 

 temperature (heating or cooling), that is effective in bringing 

 about the change. I have not yet had time to make any special 

 experiments to test this point, but I may perhaps mention that 

 such data as I possess seem rather to point to the conclusion that 

 long-continued steady heating is more effective than alternate 

 heating or cooling. As the following experiment, made about a 

 year ago, seems to bear on the point, I give the results : — 



31 6 6 



Total 



rise of 



zero 



j- i°"6 o°*i5 o°'85 o°'5 o°"i i°'2 0° 0° /^'i, 



Approximate 

 time in hours. 

 Rise of zero- 

 point 



Two other thermometers, heated each day for about six hours, 

 showed after nine days rises of zero-point of 3°"8 and 4°*i re- 

 spectively, but in these cases the change was apparently not 

 quite complete. The temperature was in each case 280°, and 

 all these thermometers belonged to the same batch as those 

 employed in my experiments already described in Nature, 



Prof. Mills does not regard the experiments as conclusive, but 

 criticizes my results in the following words : " The zero move- 

 ment, however, only ranged from 1° to i°'2 — small readings 

 which might very possibly have been obtained, or not, on either 

 of the thermometers at other times." This criticism, in striking 

 contrast to the rest of the letter, appears to be rather unkind 

 either to me or to my thermometers, I hardly know which, I 

 sincerely hope that none of my thermometers are capable of such 

 erratic behaviour as to show changes of zero-point of 1° (or even 

 twice this amount if the plastic theory is correct) without extra- 

 ordinary treatment, or that my readings of temperature are 

 reliable only to within i° or so. But to make the matter more 

 certain, I will continue the heating of the two thermometers, A 

 and C, under the same conditions as before, and will also heat 

 two more thermometers under similar conditions to about 360°. 

 Prof, Mills mentions the very curious behaviour of lead-glass 

 thermometers at different temperatures, but his objection on that 

 score to the temperature 280° does not seem to apply, as my 

 thermometers are all made of soft German soda-glass. It may, 

 however, be useful to heat two more thermometers to a tempera- 

 ture of about 220° in order to compare the total rise with that at 

 280° and 360°, 



With regard to the statement that the final state of a thermo- 

 meter kept at the ordinary temperature for an infinite time 

 would differ from that of the same thermometer after being sub- 

 jected to prolonged heating at a high temperature, I am not 

 prepared to give a decided opinion either one way or the other, 

 but it does appear to me to be rather a daring procedure to 

 make observations of the minute changes of zero-point over a 

 few years, and to extrapolate from a decade or so to eternity. 



