Dec. 9, 1875] 



NATURE 



119 



ployed for giving the radiant energy of the sun's rays acts upon 

 the following principle : — In the first place the instrument is 

 sheltered from the sun, but exposed to the clear sky, say for five 

 minutes. Let the heat so lost be termed r. Secondly, the in- 

 strument is turned to the sun for five minutes. Let the heat so 

 gained be termed R. Thirdly, the instrument being now hotter 

 than it was in the first operation, is turned once more so as to 

 be exposed to the clear sky for five minutes while it is shielded 

 from the sun. Let the heat so lost be termed r'. It thus 

 appears that r denotes the heat lest by convection and radiation 

 united, when the instrument, before being heated by the sun, is 

 exposed for five minutes to the clear sky, while / denotes the 

 heat lost by these same two operations by a similar exposure 

 after the instrument has been heated by the sun ; and it is 

 assumed that the heat lost from these two causes during the time 

 when the instrument is being heated by the sun will be a mean 

 between r and /, and hence that the whole effect of the sun's 



rays will be in reality R + ^ — ■ — . Now although this assump- 



2 

 tion may in the average of a great number of experiments repre- 

 sent the truth, yet in many individual cases it may be far from 

 being true. It would therefore seem to be desirable to get rid of 

 this uncertainty by constmcting an instrument in which we are 

 sure that the causes of variability are not allowed to operate. 

 These causes of variability I have attempted to get rid of in the 

 following manner. With the help of Mr. Jordan, mechanician 

 at Oweps College, the following instrument has been constructed. 

 It consists of a large mercurial thermometer with its bulb in the 

 middle of a cubical cast-iron chamber, this chamber being of 

 such massive material that its temperature will remain sensibly 

 ■constant for some time. The chamber with its thermometer has 



a motion in azimuth round a vertical axis A, and also a motion 

 in altitude round a horizontal axis B. A 3-inch lens C of 12 

 inches focal length is attached by means of a rod to the cubical 

 chamber, so as to move with it. The nature of this attachment 

 will be seen in the figure. Thus the whole instrument may be 

 easily moved into such a position that the lens, as well as the 

 upper side of the chamber which is parallel to the plane of the 

 lens, may face the sun, and an image of the sun be thrown 

 throiigh the hole D in the side of the chamber upon the ther- 

 mometer bulb E. The stem of the thermometer protrudes from 

 the chamber as in the figure. A screw S, somewhat larger in 

 diameter than the bulb of the thermometer, is made use of to 

 attach the thermometer to its enclosure, and a smaller screw S', 

 pressing home upon india-rubber washers, enables the thermo- 

 meter to be properly adjusted and kept tight when in adjust, 

 ment. In the present instrument the internal diameter of the 

 chamber is two inches, while the bulb of the thermometer is about 

 i^ inches in diameter. The scale of the thermometer is very 

 open, more than an inch going to one degree. I have generally 

 allowed the image of the sun given by the lens to heat the ther- 

 mometer bulb for one minute, during which time an increase 

 of temperature, not exceeding in any case two degrees, has 

 been produced. As far as principle is concerned there appears 



to be no objection to the present instrument ; nevertheless it is 

 open to a very serious pract'cal objection. The scale being so 

 very open, the stem comprehends only a few degrees ; fre- 

 quently, therefore, the temperature is such that the extremity of 

 the mercurial column is either below or above the stem. Now 

 the thermometer has a small upper chamber, and by means of a 

 method of manipulation well known to those who work with 

 thermometers, it is possible to add to or take away from the 

 main body of mercury in the bulb, so as to keep the end of the 

 mercurial column always in the stem. But experience has con- 

 vinced me that for a thermometer with such a large bulb, fre- 

 quent manipulation of this kind is not unattended with danger to 

 the bulb. On this account the instrument in its present form is, I 

 conceive, unsuited for steady work in an observatory from year 

 to year. It is however possible, without any appreciable sacri- 

 fice of the scientific principle of the instnmient, to alter it in 

 such a manner as to remedy this defect. Without altering the 

 size of the bulb, I should propose for a permanent instrument a 

 stem say eighteen inches long with a bore of such diameter that 

 the stem should embrace a range of temperature between 20" Fahr. 

 and 92° Fahr. Thus somewhat less than five degrees will go to 

 the inch. The stem might be protected from the risk of accident 

 by an appropriate shield. Let such a thermometer be heated for 

 two minutes and the size of the lens be somewhat increased. In 

 this case a rise of something like 5° Fahr. will be obtained, and 

 this heating effect might very easily be estimated to one him- 

 dredth of the whole, while the same thermometer would serve 

 for all the temperatures likely to occur in these islands during 

 the course of the year. I ought to add that a pasteboard cover, 

 gilded on the outside, is made to surround the chamber, and also 

 that between the lens and the chamber there is a pasteboard 

 shield with a hole in it to permit the fiill rays from the lens to 

 pass — the object of this shield being to prevent rays from the sun 

 or sky from reaching the instrument. In such an instrument r, or 

 the change taking place in the thermometer before exposure to the 

 sun, will in all probability completely disappear, while / will be 

 extremely smaU. At any rate we may be quite certain that 



R + will accurately represent the heating effect of the sun. 



We may probably suppose that in the same instnmaent the lens 

 (which must always be kept clean) will always stop the same or 

 nearly the same proportion ot the solar rays. But the lens of 

 one instrument may not stop the same proportion as that of 

 another instrument. This, however, is no objection if it be 

 borne in mind that the instrument is a differential one. In prac- 

 tice there would be some standard instrument which would be 

 retained at a central observatory, and all other instruments 

 would, before being issued, be compared with it. It would be 

 thus possible to compare together the indications of various in- 

 struments working in different places, provided that these before 

 being issued had their co-efiicients determined at the central 

 observatory. — On a colorimetric method for determining small 

 quantities of copper, by Thomas Camelley, F.C.S., Demon- 

 strator in the Chemical Laboratory of Owens College. Com- 

 municated by Prof. H. E. Roscoe, F.R.S. 



Berlin 

 German Chemical Society, Nov, 22.— A. W. Hofmann, 

 president, in the chair. — V. Gomp-Besanez has discovered dia- 

 static ferments, transforming fibrine and albumin into peptones 

 in malt and in linseed ; and hemp-seed, proving thereby a hypo- 

 thesis of Hooker and Darwin respecting the power of plants for 

 dissolving starch, &c (expressed ^in Darwin's "Insectivorous 

 Plants," p. 362). — F. Salomon, in a paper on the formation of 

 anhydrides in chemical reactions, tries to explain why sulpho- 

 carbonate of ethyl treated with methylate of potassium yields 

 sulphocarbonate of methyl, whUe vice versd sulphocarbonate of 

 methyl and ethylate of potassium yield sulphocarbonate of ethyl. 

 He supposes that in these reactions CSO is set free and reacts on 

 methylate or on ethylate of potassium. — H. Skraup described a 

 pioduct of the action of chlorine on ferricyanide of potassium, 

 perhaps FeCygKg. — L. Barth has obtained a ferrocyanide of 

 tetramethylammonium (yellow crystals) by saturating ferrocyanic 

 acid with tetramethylammonium-hydrate. — L. Barth and C. 

 Senhofer, in preparing disulphobenzolic acid, have foimd this 

 acid to be, when prepared at a moderate temperature, meladi- 

 sulphobenzolic acid, at a higher temperature paradisulpholxn- 

 zolic acid ; the former yielding isophtalic, the latter tercphtiialic 

 acid; both, however, by fusion with potash yielding resortine, 

 — C. Senhofer has prepared naphthalintetrasulphurous acid, 

 CioH4(S03H)4, by treating naphthalin with oil of vitriol and 



