JlXE 14, 1895.] 



SCIENCE. 



07 1 



On the Absorption of Certain Crystah in the 

 Infra-red as Dependent Upon the Direction of 

 the Plane of Polarization. By Eexest Mee- 



RITT. 



By means of a spectro-bolometer the 

 writer has determiued the transmission 

 curves for Quartz, loehiud Spar, and Tur- 

 malin ont to a wave length of 5.5 /i. lu 

 order to detect the difterences between the 

 absorption of the ordiuaiy and extraordinary 

 rays the radiation used (that of a Zirconium 

 lamp) was polarized by reflection l)efoi-e 

 passing through the crystal specimen. On 

 account of difl'use rays fi-om the surface of 

 the fiuorite prism considerable difticulty 

 was met with in obtaining a pure spectrum; 

 a difficult}' which was finally met by using 

 two spectrometers 'in series;' i. e., the 

 •spectrum formed l>y one spectrometer was 

 thrown upon the slit of another. The re- 

 sults show that the transmission curves of 

 the ordinary and extraordinary rays are 

 entirely independent in all three cases. In 

 the case of Iceland Spar the differences be- 

 tween the two curves is especially marked, 

 sharp absorption bauds being present in the 

 one curve which are entirely absent in the 

 other. At / = 3. .3 fi Iceland Spar is found 

 to behave as turmaliu, ;. e.. the ordinarj- ray 

 is suppressed, while the extraordinary ray 

 is transmitted in considerable amount. The 

 difference between the two curves is less 

 marked in the case of Quartz, but is very 

 considerable with Turmaliu. In the latter 

 case the two curves are found to intersect, 

 and in the region lying between the points 

 of intersection the dechroism of turmalin is 

 revereed. 



PeMnance in Transformer Circuitg. By F. 



Bedell and A. C. Ceehore. 



In tliis article the writers discu.ss the 

 action of a condenser in either circuit of a 

 transformer, and develop by iHirely graphical 

 methods the conditions necessary for primary 

 resonance due to a secondary condenser, a 



phenomenon to which Dr. Pupiu has given 

 the name electrical con.sonance. A primary 

 circuit alone, and with no condenser, would 

 have no natural period of oscillation; but 

 it may have such a period when a neighbor- 

 ing secondary circuit contains a condenser. 

 The elastic influence of the condenser is 

 transferred from one circuit to the other, 

 on account of their mutual relationship; 

 and the natural period of the primary cir- 

 cuit depends not only upon the value of its 

 own constants, but tlio.se of the .secondary 

 as well. There is a surging of energy back 

 and forth between the primarj- circuit and 

 the secondary condenser by intervention 

 of their common magnetic field ; the 

 period of these surgings determines the 

 period of the system. In addition to the 

 graphical analysis, Drs. Bedell and Cre- 

 bore subject the problem to a brief analyt- 

 ical treatment leading to identical results. 

 It is shown that there are two values of 

 the capacity of the secondary condenser 

 which will give rise to consonance. It is 

 pointed out that a condenser in the second- 

 ary of the transformer maj- compensate 

 for the drop due to magnetic leakage ; 

 in fact, this drop maj- be over-compen- 

 sated for, so that the secondary poten- 

 tial will actually rise as the transfoi-mer 

 is loaded down. 



Aside from the particular conclusions 

 reached, the paper is of interest for the 

 methods employed, the problem in hand 

 illustrating well the writer's method of re- 

 ciprocal points in constructing admittance 

 and current diagrams from diagrams of 

 impedance and electromotive forces. 



On the Secidur Motion of a Free Magnetic 



Needle, I. By L. A. Bauer. 



This article forms the introduction to an 

 important paper on the secular variation 

 of terrestrial magnetism which will be con- 

 cluded in the next number. The present 

 article is devoted to a description of the 



