November 15, 19 17] 



NATURE 



213 



perature at which steel is poured, as the properties of 

 the ingot produced are influenced by this factor. The 

 correct measurement of this temperature is difficult; 

 thus, if an optical pyrometer be sighted on the molten 

 stream as it issues from the furnace, black-body con- 

 ditions are not realised, and the apparent temperature 

 indicated may vary according to the quantity of slag 

 accompanying the metal. Similarly, the layer of cooled 

 slag on the surface of the metal in the ladle prevents 

 the true temperature from being ascertained by optical 

 means. Although an occasional reading may be taken 

 with a sheathed junction of platinum and platinum- 

 iridium alloy, the method could not be used regularly 

 owing to the rapid destruction of the sheath. One pro- 

 posal made was to encase the wires in a large mass of 

 fireclay, leaving the ends uncovered, so that both 

 touched the molten steel ; but it was pointed out that 

 this method would cause a rapid destruction of the 

 wires. In spite of these difficulties much progress has 

 been made by following out definite lines of procedure, 

 such as sighting on a certain part of the molten 

 stream at definite intervals of time during the pouring. 

 Mr. Cosmo Johns and others found it possible, under 

 uniform conditions, to obtain readings varying only 

 by 5"^ to 10°, which, as the chairman remarked, was a 

 surprising result considering the temperature measured. 

 All the speakers who had attacked this problem agreed 

 that the temperature of open-hearth stee! when being 

 poured was about 1600° C, careful determinations by 

 Dr. Hatfield with a thermal junction indicating 1600° 

 to 1625°. Further work in this direction is very desir- 

 able, as a trustworthy method would be of the greatest 

 value to the steel-maker. 



It is still customary in the pottery industry to gauge 

 the firing temperature by using a set of clays or pro- 

 gressive fusibility, and noting the effects on the separate 

 pieces. The latest developments of this method were 

 described in the paper read by Mr. H. Watkin, one 

 of which consisted in placing the test-pieces across two 

 sloping uprights, ladder fashion, so that the droop or 

 complete fusion of any could be readily observed. 



Two new suggestions for measuring temperatures of 

 the nature of 1600° C. were put forward, both of which 

 entailed the use of a fused metal. Dr. Northrup, of 

 Trenton, U.S.A., described an instrument based on 

 the expansion of molten tin, constructed on the same 

 lines as an ordinary thermometer. The bulb and stem 

 were of graphite, and a nickel wire passing through a 

 gland in the top of the stem could be pushed down so 

 as to touch the top of the molten tin, when an electric 

 circuit was completed. The position of the top of the 

 column of tin in the stem could thus be ascertained and 

 the stem divided up in the same manner as a thermo- 

 meter. Dufour many years ago suggested a thermo- 

 meter of tin in a silica envelope, but the instrument 

 never came into practical use, and the graphite en- 

 closure is an undoubted improvement. Dr. Northrup 

 has found that molten tin does not give off vapour at 

 1700° C, and proposes to use his instrument up to 

 this or even higher temperatures. Mr. C. R. Darling 

 suggested a thermo-electric pyrometer in which one or 

 both of the members of the couple might melt without 

 breaking the circuit. As shown by Mr. A. W. Grace and 

 Mr. Darling, the thermo-electric properties of metals in 

 general are unchanged by fusion, and hence cheap 

 metals, such as tin or copper, might be used to measure 

 temperatures of 1500° C. or more, as their boiling 

 points usually exceed 2000° C. 



An excellent feature of the meeting was an exhibition 

 in the room of pvrometric apparatus of all kinds. In- 

 cluded in these was the original tapered gauge used by 

 Josiah Wedgwood for measuring the contraction of his 

 clay cylinders, by means of which the science of high- 

 temperature measurement was founded. The modern 

 productions of British makers are highly satisfactory, 



NO. 2507, VOL. 100] 



and this young but flourishing industry has undoubtedly 

 a great future in front of it. Special mention may- be 

 made of an automatically controlled furnace, on the 

 principle devised by Mr. R. P. Brown, of Philadelphia, 

 The control is effected by means of a thermo-electric 

 pyrometer inserted in the furnace, the indicator of 

 which is provided with two stops, which may be set in. 

 any position, one on either side of the pointer. To 

 control a furnace to within 5° above or below a given 

 temperature, the stops are set at 5° on either side of 

 the number on the indicator. The pointer of the indi- 

 cator is depressed periodically by means of clockwork, 

 and when touching either stop an electric circuit is 

 completed which actuates a relay. If touching the 

 lower stop, the effect is to cut out an external resistance 

 from an electric furnace, or to open wider the tap of 

 a gas supply in a gas furnace, whilst when in contact 

 with the higher stop resistance is added or the gas 

 supply checked. There appears to be no good reason 

 why large furnaces should not be similarly controlled; 

 and the saving in fuel and labour effected should soon 

 cover the cost of the apparatus. 



The success of the discussion, in which makers of 

 pyrometers, representatives of various industries, and 

 scientific men were able to compare notes, suggests 

 that meetings of this kind are desirable in connection 

 with the application of science to manufacturing pro- 

 cesses, and cannot fail to act as a stimulus to all con«- 

 eerned. 



HEREDITARY CHARACTERS IN RELATION 

 TO EVOLUTION.^ 



(i) T7 IRST, then, what are the facts as to numerous 

 -^ finely graded variations in a single unit factor? 

 Here we have certain remarkable data as to the eye- 

 colour of Drosophila — data that are of great interest 

 witli relation to the nature of evolutionary change. This 

 fruit fly has normally a red eye. Some years ago a 

 variation occurred by which the eye lost its colour, 

 becoming white, a typical mutation. Somewhat later, 

 another variation came, by which the eye colour be- 

 came eosin. By those wonderfully ingenious methods 

 which the advanced state of knowledge of the genetics 

 of Drosophila have made possible, it was determined 

 that the mutations white and eosin are due to changes 

 in a particular part of a particular chromosome, 

 namely, of the so-called X-chromosome, or chromo- 

 some I. And further, it was discovered that the two 

 colours are due to different conditions of the same 

 locus of the chromosome; in other words, they repre- 

 sent two different variations of the same unit. More- 

 over, the normal red colour represents a third condi- 

 tion of that same unit. And now, with the minute 

 attention paid to the distinction of these grades of 

 eye colour, new grades begin to come fast. Up to 

 date we know from the mutationists' own studies of 

 Drosophila that a single unit factor presents seven 

 gradations of colour between white and red, each 

 g-radation heritable in the usual Mendelian manner. 

 These grades are the following: — (i) red; (2) blood; 

 (3) cherry; (4) eosin; (5) buff; (6) tinged; (7) white. 

 Considering that the work on Drosophila has been 

 going on only about seven or eight years, this is 

 remarkable progress toward a demonstration that a 

 single unit factor can present as many grades as can 

 be distinguished ; that the grades may give a prag- 

 matically continuous series. The extreme selectionist 

 asks only a little more than this. 



Besides showing that a unit factor may thus exist 

 in numerous minutely differing grades, this case shows 



1 Abridged from an address by Prof. H. S. Jennings. Continued from 

 p. 198. 



