416 Scientific Intelligence, 
seven hundred lines more refrangible than H, 9 from among 
them, for the sake of comparison, the lines L, , O, P, Q, R, already 
employed by physicists, as well as two others, S ai T, still more refran-_ 
gible and not previously studied. The wave- lengths were determined by” 
means of a ruled glass, executed by No bert, and containing about 44 lines 
to the millimeter. The following tabls gives the results of the measure- 
ments in thousandths of a millimeter 
B 068667 F 0:48596 N  0°35802 
C 065607 G 0743075 O 034401 
D_ 068880 H 0°39672 P = 0°33602 
E 052678 L 0°38190 Q  0°32856 
&b 051655 M 0°37288 R 031775 
numbers contained in this table are the means of ten series of 
experiments which closely agreed. The author believes them exact to at 
least half a unit in the fourth significant figure, exzept in the case of the 
ultra-violet rays where the observation is more difficult. The numbers 
are in a little higher than those of Fraunhofer in his second series. 
— Comp ndus, \wiii, 1111. 
2. On ‘the determination of wave lengths by means of interference iodide 
—Bernarp has re-invented and presented to the Academy of Sciences 
which the solar lines could be seen. If m be the eae of bands com 
prised between two rays corresponding to the wave-lengths 4 and #, 
and 8’ the differences between the — and extraordinary indices for 
these rays, and e the thickness of the plate, the value of 4 may be de- 
—, in which m is to be taken as positive 
duced from the equation 4= 5 
or negative according as 4 is smaller or greater than i’. To determine the 
wave-length of any line in the spectrum, it is therefore only necessary to 
know a single wave-length, as for instance that of D, and the uantities 
5, 0’, e, given directly by observation and determined once for all for the 
same whee = is —_ necessary to count the test of included lines me 
rays is produced by a plate of quartz 0°999"™ 12 
oh "Tipe seach by wax to ssaideenmbics as to cover 
be ‘ 
