132 



KNOWLEDGE 



[June, 1902. 



iiml fiivcs a table showiiii; tho Iioiglit on his insiruinont at 

 whieli Iho diffoveut liquids Iwili'd — 



•' In Inijus talmlce colunina prima lialicnlurpjraduscaloris 

 in pr(.i>ortione aritUmetioa conijnitum inrhwindo a calorc 

 (|\iii arjiia incipit gelu rigescoro tanfjnani ab infiiiio naloris 

 •jradu sou commune termino calovis ot fvigoris, ct ])oncndo 

 calovom oxtornum corporis bumani esse jiarlium dnodi^cim. 



" Patet auteni per hanc tabulam quod calor aquic bullien- 

 lis sit fere triple major qiiam calor corporis liumani. 



" Ex Lis invtntis poncndo oalores olei ipsius rarefactioni 

 ]>roportionuleset pro calorecorporishunianiscribendo])artes 

 12 piodiit calor aqu£B ubi incii)it ebullire partium 33." 



(In the first column we have that degree in which water 

 begins to freeze as the lowest degree, making the external 

 heat of the human body to be 12 degrees. Now it is evident 

 from this table that the heat of boiling water is almost 

 three times that of the human body, being 33 degrees.) 



In the article on heat in the Encyclopedia Bniannica 

 by Dr. Mill, late Librarian to the Royal Geographical 

 Society, the writer mentions the paper by Newton, and 

 then describes the thermometer by Fahrenheit, who took 

 his predecessor's scale as his improved standard. After 

 writing this, I had an interview with Dr. Mill, who in- 

 formed me that from the researches he made at the time 

 of writing his article he certainly came to the conclusion 

 that this was the ease, that Fahrenheit copied Newton. 



I also enquired of Mr. E. H. Scott, f.b.s., the late 

 Secretary of the Meteorological Council, and he gave me 

 a piaper he had written in 1884 in which he says : " We 

 next come to Newton, and in the Philosophical Transictions 

 for 1701 we find a paper, certainly from his pen, on the 

 scales of thermometers, and in it he announces that his 

 instrument, tilled with linseed oil, is marked 12 at the 

 temperature of man's blood. This is the first notice we 

 possess of a blood heat ' on the scale.' Fahrenheit 

 began by using a scale of minus 90 and plus 90 blood 

 heat. This scale he soon gave up, by Boerhaave's advice, 

 for one with 24 for blood heat. He then divided these 

 degrees into quarters, and this gave him 96 for blood 

 heat. Carrying on his researches he found that water 

 boiled at 212. Such was the origin of the famous Fahren- 

 heit .scale." 



In the Philosophical Transactio7is for January, 1724. is 

 a short ]iaper, entitled "Experimeuta circa gradum caloris 

 liquorum uonnullorum ebullientium instituta; a Dauiele 

 Gab. Fahrenheit." The author alludes to the experiment 

 of another chemist, that water boiled at a fixed point (tixo 

 gradu 212°). This he himself confirmed, as well as in 

 most other liquids of which he gives a table. He used 

 mercury as it answered so well in the l)arometer. I 

 lielieve most authorities give Fahrenheit credit for first 

 using mercury for a thermometer. 



Now I may mention Renou, to whose opinion Mr. Abbe 

 evidently attaches much importance. He says : — 



" On trouve dans les Philosophical Transactions pour 

 1701, un article anonyme mais qu'on sait C'tre de Newton. 

 " L'echelle des degres de chaleur." 



" Cette article donne les points de fusion et d'ebullition 

 d'un grand nombre de corps, evalucs avec tin thermometre 

 a I'huile de liu qui marquant 0*^ a la temperature de 

 congelation de I'eau, 12° a la chaleur du sang humain, et 

 34° a la plus violeute ebullition de I'eau. C'est le 

 premiere indication que je trouve dcla chaleur du sang de 

 I'homme : on aitribue ordinairemeut a Boerhaave la 

 decouverte de la fixite de cette temperature ; je ne sait si 

 ce fait est certain." " Nous avons dit tout a I'heure que 

 Ne^vton avait evidemment pris pour I'un des [loints fixes 

 de son thermometre la temperature de sang humain ; nous 

 allons voir que, pendant lougtemps cette temperature joue 

 un role important." M. Renou then mentioned Fahren- 



heit's first thermometer, and goes on to say, "Fahrenheit 

 abandonna bii'utot ci-ttc i;chellft d'apres les conseils de 

 Boerluuive peut-i'trc et adupta peu de temps avant 1714 

 une echelle qui ne comportait que 24^ comprenant le memc 

 intervalle que son premier thermometre. Peut-etre 

 Fahrenheit n'avait il pas voulu d'eloignortropde la division 

 de Newton, mais ])0ur un intervalle jdus grand il dut 

 choisir un nombre de divisions double." 



[We find in the Philosophical Transaclions for 1701, an 

 anonymous ai'ticle known to be Newton's, on the scale f>f 

 heat. It gave tho boiling point in a number of liquids by 

 a linseed oil thermometer, beginning with freezing, makint; 

 blood heat 12 and boiling water 34. This is the first 

 indication of the heat of the human blood, and this for a 

 long time ]^layed an imjiortant part. Fahrenheit 

 abandoned his earliest thermometer, and not wishing to 

 depart from Newton's division made blood heat 24.] 



Samuei, Wilk.s. 



THE VISIBILITY OF THE CRESCENT OF VENUS. 



TO THE EDITORS OF KNOWLEDGE. 



Sirs, — Allow me to refer your two correspondents on 

 the above subject to a paper of my own in the Journal of 

 ihe British Astronomical Association, Vol. XL, p. 339, 

 where they will find Stoddart's alleged observations 

 discussed, and, I think, will conclude that Mr. Maunder 

 does that gentleman no injustice in not accepting his 

 claims as proved. 



But I think that in the note in Knowledge the powers 

 of sight required for different observations are not 

 sufficiently differentiated. The ability to see eleven stars 

 in the Pleiades, and to pick u]) Vesta and Uranus, or to 

 see Venus at mid-day, is of a different order to the ability 

 to divide El and £.3 Lyrse, to define the crescent of Venus, 

 or see the satellites of Jupiter. Of course both abilities 

 may be possessed, as in Mr. Mavmder's case, by the same 

 individual, but this is not necessarily so. 



I shall be glad to know under what circumstances 

 Jupiter's 2nd satellite can be elongated nearly 4' of arc. 

 I cannot make it more than 206" from the limb, and this 

 only in opposition. Although this is about the same 

 distance as e^ and e, Lyne, I think the great difference of 

 magnitude of Jupiter and II. makes the separation a very 

 different matter indeed. 



As regards Mr. Rodgers' instance of the visibility of the 

 crescent of Venus, it is defective in the same way as are 

 most of the astronomical feats of this kind, in that neither 

 date, hour, nor place is given, while it is also anonymous. 

 It has convinced /(/(/i, but it cannot be held sufficient to 

 convince others. Besides, most people are aware that the 

 crescent of the moon is convex towards the sun, and would 

 naturally see the crescent of Venus in the same way if the 

 observation was entirely imaginary, and when shown the 

 crescent reversed in the telescope would find it contrary to 

 their anticipations. I believe nine jtersons out of ten who 

 think they have good sight would see the crescent if one 

 asked them, if reminded it was convex to the sun. 



But Venus would be represented by a crescent -^^ of 

 an inch long at 10 inches from the eye, or a fourth of an 

 inch at 62 feet. Can any eye make out the shape of such 

 a brilliant crescent ? yet Venus would be seen tmder less 

 steady conditions than such near crescents. 



I have only been able to obtain exact date and hotir of 

 one alleged observation of a satellite of Jupiter with the 

 unaided eye, and on investigation it turns out the planet 

 was about three weeks past quadrature at the time. 



The visibihty of the crescent of Venus can be experi- 

 mented upon indoors. Let a crescent 1 in. from cusp to 

 cusp be cut out of card, and illuminated by a lamp placed 



