651 



PHYSICS, PROGRESS OF, IN 1895. 



Sanf.mlr PhjrsioU Review. NovemWr and Iv- 

 cwnber) has extended his former obeei 

 U dependence of nwHlancc Upon t In- surround- 

 ktff dielectric, which have been severe! v criti- 

 3d (-Annual C'yclopwdia," 1808. p. tWl. atul 

 vi' , , suits have !-. ntly 



been vrriftVd qunliutivrly by (irimaldi and Ca- 

 tania ' ; '' r "l- 

 per wirtv h " ihnt the amount i>f clump 



. a ri :. Mmpfei <>f wire, 



butUoonM.v: in dilMtkmte the same mate- 

 rial Thus the resistance of copper was less in 

 prtrtilriitii thnn in mr. while (hat <>f >ih 

 bii in air. Tl beht>TWof acopper-pUted >il- 

 Ver wirr wa*alm-t identical with that <>f pure 



\inerican Academx 



periroenU on the resistance of poor oondu 

 oca M different kinds of wood and stone, ob- 

 tained the following result* in megohms : 



MATERIAL. 



i: , 



u : 



Vi 



810 



17 



860 



8 



184 



610 

 IftK 



"5 



280 



The wood was all well seasoned and the resist- 

 ance was measured with the grain. Across the 

 grain it was 20 to 50 per cent, higher. The 

 tone was sun dried f-.r three weeks before test- 

 ing. Gin and 1/elcux (Paris Academy of Sci- 

 ences, April 29) find that the resistance of sac- 

 charine solutions depends on the concentration 

 and temperature, and is also a function of the 

 v. |;. C,,l.M,n (Paris Academy ..f 

 liat ohm'-, law do,- not hold in 

 ' the propagation of waves of hi^h j>o- 

 ... as from the secondary of an induction 

 coil, in high resistances, such a- threads satu- 

 rated with a solution of calcium chloride or cap- 

 illary tubes filled with water. Tuma r Wiener 

 Berfchte," June 14) has determined the 

 nee of copper. German silver, nickel, and iron 

 wires for om-illatin- currents. The results agree 

 Mill the formulas obtained by 

 Stefan, and for alternating currents of high fre- 

 quency the agreement was more complete for 

 nonmafnetiiahle conductors. 



the variability of the 



wire 



nders calculation illusionary. With iron 



". f-i-t:in.-e de<TeH-cd as 



the current 

 ftrnigtn increased. J. W. Rodger .1 

 "tabu 8, 18H the experiments of 



Kohlratmh and i r ..n the electric con- 



f pun- water, a constant for which 

 widely different values hare been found. 

 measured at IT the temperature rat' 

 r* trie* of samples of water of differer- 

 KM* of purity and aluo the condu. -tivity of two 

 Mpks of very pare water at fl . As- 



unjf that the obsenred .-..ndurtivity was re- 

 thatof pure water and a di- 

 1 invpunt r. thoy made use of t IH 



fvAner *t 18 to obtain tlie conductivity 

 < Jv rurv water, which they find 

 19 . Tk* smallest ralue actuallv <.li- 



'hat the almost infi 



*^ I impurity present changed the 



by abrit 10 per cent. Warbruu' 

 * Annalen," March) is of the opin- 



ion that the alteration of conduct ivity that is 

 prod 1 1 .-leetric current in aniline and 



similar Indies, and the cniiveetinn phen. 

 that thev exhiliit, may all ! explained 1 



them I" ' : lute >olir 



iyte. The similar ln-ha\ . 

 /.ol. I urp n! Hi' . etc., i- pi"l>al>l\ due : 



irnal '! iMiy-sique." ' 



in inve>ti^ati<.n's on the inlluem-e of m.i 

 lields,,n electrical re.i^tam . find- that il 



c in the iv-i-iance of l.^muih ol. 



withoonttaat or alternating (in i vnt- i- n, 



aide ..ui-ide a magnetic field with a fiv.ju, 

 80 a second, and can IM- deteeted in mn 



with a fre|iiem-y of only :'. ..r t. i 

 ference depend* on the frequency, and \\ 

 a Held increases with the frequen. \. Itismuih in 

 strong magnetic field-. .IT.-I-> to an inci 

 rent a greater resi-t a nee. and \ a decrea*ii. 

 . less resistance thai i that for >t.-al\ cm 

 Thediflferenceof then 

 decreasing currents increases with the i 

 change in the strenu'th. and tlii* .i 

 more marked with strong rurreiits than with 



>ties The results call II"! lie due ' 



induction, or they would occur outside a mag- 

 netic field. Printfsheim (IJerlin I'hy-ical .^ 

 April 26). from experiments on tin' cMndu 

 of heated gases, finds that the farther apart the 

 electrodes the less the current, while with con- 

 .-taut di-iance the current decreases \\iih the 

 time. Polarization was quite percept illc for a 

 half hour after breaking the current. 11 

 eludes that the phenomenon i> elect: 

 Viiieentini and Cinelli ( Nuovo Ciment. . 

 \\.\VI. No. 3) have experimented on ih. 



i-icity through th- L'a- Mirround- 

 inga wire made red hot ly an electric n, 



-nits depend on the ffas and show, in the 

 opinion of the authors, that in the en 

 gen the gaseous molecules that leave t he 

 of an incandescent platinum wire are po- 

 electrified, their potential In-ini; alioiit . 

 higher than the mean potential of ih- 

 With air and carl >on dioxide the excess i 

 greater, being al. ut 1 volt. With h\dr< ... 

 a hitfh temperature an inversion of the pi, 

 eiion takes pla<-e. .1. .1. Thomson (Tan, 

 riiilosophical Society, Feb. 11) has dc\ 

 method of measuring the conductivity of l.adly 

 conducting substances by placing a -p! 

 the substance to lie measured \\itliin a coil that 

 is traversed by rapidly alternating cun-ei, 

 second coil connected "in >erie* with the f 

 closes an exhausted Imlh. The introduc: 

 the sphere into the first coil causes by in'! 

 a change in the currents, and hence an 

 tion in the j;low of the I. nil., l.y o|,x ( .r\in- 

 the ^phere'x conductivity is olitained. IJranly 

 (Pans Aea.lemy 



n pairs o'f metals, as c |>| 

 contact resistance. 



<ffic Induct;,, Capacity. Pc]\&\ r .Jour- 

 nal dc Physique," NovemLen has devised an in- 

 strument for n, fie induct : 



pacity in either liquids or solids It 

 essentially of two attracted di-k electrometers 

 in which "the two moval.le disk- are ri^ii: 

 nected. and tlie two attract in^ disks are electric- 

 ally connected ; one of the latter is movaldc hy a 

 micrometer screw. The two former are at ; 



