142 



SCIENTIFIC INTELLIGENCE. 



[185:3. 



the seusitive bath, I pluuge it fairly into the bath, ^vhere it is left to 

 soak fur tire ur six luiuules ; then lemoviug it wash it Ibrabout twenty 

 minutes iu a b;ith, oj- even f,vo, of clistiUed waler, to remove the excess 

 of uii.ate of siirer ; and then haug it up to dry (in lieu of drying it 

 with bliitting paper). Fape.- thus prepared possesses a greater uagree 

 of sensitiveness than waxetl paper ; and preserves itsseusitiveuei-s, not 

 so lung as waxed paper, but sutticieutly long for all praotieal purposes, 

 say thirty hours, and even in )ie. The English manufactured paper is 

 far supciiur for this purpose to the I'^ieucli. To develupe these views, 

 a few drops of the solution of niti'ate of silver are required in the gallic 

 aeid bath. They are then finally fixed and waxed as usual. 



These processes appear to me to be reduced to nearly as great a de- 

 gree of simplicity as possible. I am never troubled with stains or spots, 

 and there is a regularity and certainty in the results that are very satis- 

 factory. You will have observed, too, "how perfectly the aerial perspec- 

 tive and gradation of tints are preserved, as also how well the deepest 

 shadows are penetrated and deveh)ped, speaking, in fact, as they do, 

 to the eye itself in nature. In exposing for landscape, I throw aside 

 all cousideiatiou of the bright lights, and limit the time with reference 

 entiiely to the dark and feebly -lighted pai-ts of the view. With a 

 3}4-iuch lens the time of exposure has thus vaiied from ten minutes to 

 an hour and a half, and the action appears to me never to have ceased. 



The influence of the air-pump in this appears to me very sensible, 

 and deserving of further examination and extension. I purpose not 

 ouh' iodizing, but rendering the paper sensitive with the action of the 

 air-pump, by perhaps suspending the sheet after immeision in the 

 nitrate bath under the receiver of the air-pump for a few minutes 

 before exposure in tlie camera, or by some other manoeuvre having the 

 same object in view. 



I should add, that I have chiefly employed Canson's French paper 

 in iodizing with the aid of the pump. Few of the English manufac- 

 tured papeis are sutilcieutly tenacious in their sizing to resist the action 

 of the pump, but they may easily be made so ; and were, iu short, the 

 English paper, so far superior in quality to the French, only better 

 sized, — that is with glue less easily soluble, even though more impure, 

 there is scarcely any limit to the beauty of the views that might be 

 produced. 



There are more minor details that might be given ; but I fear 

 repeating many a "twice-told tale," acquainted so little as I am with 

 what is doing : the preceding, however, may have some interest, and 

 whatever is of value is entirely due to our friend M. Regnault, ever so 

 generously ready as well as able to aid and encourage one's etforts. 



Ever yours. 



JOHN STEWART. 



Clemistry and Physics. 



1. On the motion of Fluids from the Positive to the Negative Pole of the 

 closed Galvanic Circuit. — Wiedemann has communicated to the Prussian 

 Academy ot Sciences, a memoir on the mechanical action of the voltaic 

 circuit which is of essential interest and importance. The apparatus 

 employed consisted of a porous eai'tlienware cell, closed at the bottom 

 and terminated above by a glass bell firmly cemented to the upper 

 edge of the cylinder. Into the tubuture of the bell a vertical glass 

 tub.-: was titted, from which a horizontal tube proceeded so as to permit 

 the fluid raised to flow over into an appropriately placed vessel. A 

 wire serving as the negative pole of a battery passed down through 

 the glass bell into the interior of the porous cylinder, where it termina- 

 ted in a plate of platinum or copper. Outside the porous cylinder 

 another plate of platinum was placed and connected with the positive 

 pole of the battery. The whole stood iu a large glass vessel, which, 

 as well as the interior porous cylinder, was filled with water. The 

 intensity of the current was measured by a galvanometer. As soon as 

 the cii'cuit was closed, the liquid rose iu the porous cylinder and flowed 

 out from the horizontal tube into a weighed vessel. The results ob- 

 tained by means of this apparatus were as follows : — 



(I.) The quantity of fluid which flows out in equal times is directly 

 proportional to the intensity of the current. 



(2.) Under otherwise equal conditions, the quantities of fluid flowing 

 out are independent of the magnitude of the conducting porous surface. 



To avoid auy uncertainty arising from the laws of the flow of liquids 

 through small oriflecs, Wiedemann measured the iiitnisity of the 

 mechanical action of the current by deterniiniiic,' tlio luiLclit ofacolumu 

 of mercury which would hold the trausfc! ring force iu e(|iiilibrium. For 

 this pur|K]se a gradu.ile.l tube ur maniinieler tilled witli niercnrv was 

 attarh.Ml ioil„.,.x:ivi,iiiv of tli ■ li.iri:a>ut;d tube above nienlinnecl :" with 

 ditr.-rrhl run-riit-, :iri<l porous surfaces of (lilicroul extent, tlie niercnrv 

 iu tlif iii:oio,nel..r n,s,. lo diir.Tcul heights. Hy the measurements of 

 these heights the following results were obtaineil : — 



(3.) The height to which a galvanic current causes a fluid to rise, is 

 directly proportional to the intensity of the current and inversely pro- 

 . portioiiaf to the extent of the free porous surface. 



The mechanical action of a galvanic current may also be referred to 

 its simplest principles by the following proposition : — 



(4.) The force with which an electric tension, present upon both 

 sides of a section of auy given fluid, urges the fluid from the positive 

 to the negative side, is equivalent to a hydrostatic pressure which is 

 directly proportional to that teusiou. 



In this manner therefore we obtain a simple measure of eleebic ten- 

 sion and its niechauical actiou iu terms of atmospheric pressure and 

 consequently of gravity. 



The above laws hold good only forfluidsof the same nature. When 

 difl'erent fluids are sulijected to the actir]n of the currents, the mechan- 

 ical actiou is greatest upon those which oppose the gieatcst resistance 

 to its passage. The requisite data are still wanting to determine the 

 precise connection between the mechanical action and the resistance, 

 but observations made witli solutions of sulphate of copper of different 

 degrees of concentration, appear to show that the quantities of fluid 

 ti-ausferred iu equal times by currents of equal intensity, aie nearly 

 proport oual to the squares of the resistances. — Monatsbo-ricld dcr K P. 

 AkaiU-mic dor Wisscnschaftcn, March, 1852, 151. 



Spots on the Sun. — The number of spots seen in 1826 was 118; from 

 this there was an increase to 161 iu lb27 and 225 in 1828, and tiien a 

 decrease to 33 in 1833. The number agaiu increased, and was 333 in 

 1837, 282 in 1838, and 34 iu 1843. Again it increased aud after Ave 

 years in 1848. it was 330, since which there has again been a decrease. 

 Moreover at the time of minimum the sjjots aie much smaller than at 

 the maximum. In 1844 tlie largest was hardly 4' broad. WhUc ia 

 1848 three groups were 83^3' across, and one spot appeai'ed for seven or 

 eight cousecutive rotations. 



il. Gautier observes that he has remarked a singular connection 

 between this decennial period in the spots, and a deceunial period in 

 the variations of the magnetic needle recently pointed out by Dr. 

 Lament of JIuuich. According to this astronomer, since August, 1840, 

 the mean annual amplitude of the diurnal variation of magnetic decli- 

 nation between 8 a. ji. aud 1 p. m. augments regularly fur five j'ears aud 

 then diminishes for five years. The epoch of the minimnm of this 

 amplitude corresponds to the middle of the year 1843, aud that of the 

 maximum to the middle of 1848. He has also found, from the Gottiu- 

 geu observations a maximum in 1837, corresponding with the above 

 observations on the spots. 



The results of Dr. Lament have been confirmed by M. Reslhuber at 

 the Observatory of Kremsmuuster in Austria. Thus in 1843, the 

 annual meau diurnal variations of declination and intensity have been 

 respectively 6' 28"-6 aud -\- 0-00088; and m 1844 they were 6' 14'- 9 

 and + 0-00138. In 1848, they ware 10'o5"-4and -\- 0-00273 ; in 1849, 

 10' 39".5 aud and 0-00230. 



M. Schwabe has deduoed from eight observations with regard to the 

 period of rotation of the sun, 25-07 days as the shortest, 25,75 as the 

 longest : the mean of his results gives 25-507. He remarks that some 

 of the spots have a brownish red coloiu- ; one was examined with 

 glasses of different colours, to avoid any source of error, its north side 

 was reddish-brown, more red than brown. The next day it had much 

 changed and the border had the usual gray colour. 



M. Rodolphe Wolf, of Berne, has been registering the spots since 

 1847 ; and he concludes that the number through a year so varies, that 

 if a curve be drawn to express the va; iation, this curve has umlulations, 

 the more regular of which correspond each to a perioil of about 27tj 

 days, or the period of the snn's rotation with 1 elation to the earth. As 

 bearing on this subject, the author states that M. Buijs BaDot of 

 Utrecht, has concluded from thermomctric observations at Harlem, 

 Zwaneubourg and Dantzig, (see Fogg. Ann., 1851, Dec) that during a 

 number of years, at each period of 27-7 days there is at these places a 

 small elevation of temperature and at the intermediate period a 

 diminution. 



On the Freezing of Vegetables. — In connection with an abstract of Pro£ 

 J. LeConte's paper" On the Freezing of N'egetables, (Sillimau's Journal, 

 vol. xiii., 84,) published iu the BibliothequeUniversellefor June, 18.52, 

 the following note is inserted by M. A. de Candolle, showing that the 

 action of freezing on vegetation for some years has not been altogether 

 misunderstood by botaiiist.s. "In 1838, I published in the Bulletin de 

 la Classe d'Agriculturc de Geneve (No. 121, p. 171,) in an article 011 

 tlie intense cold of January, 1838, the following remarks — after first 

 alluding to the observations of Pictet .and Maurice who found the 

 tenij-ieratnre of the centre of a chesnnt tree below zero, and also the 

 experiments of M. Ch. Coindet, who after a prolonged cold had ex- 

 tracted (VoiM the niiildle of a large tree, small crystals of ice : — "These 

 treis arrhwxvver not dead. I have myself, after a cold but little 

 iiikiise, sreii crystals of ice in the irterior of the buds of several trees 

 wliieli have not suffered from it. Young branches, the buds of many 

 tiees. and the leaves of the plants of our country are in winter often 

 peni4rated beyond doubt with a cold several degrees l)elow zero 

 (centigrade) ; and although the viscous liquids of the slender tubes 

 congeal with difficulty, it must frequently happen that congelation 



