196 W. Gibbs on the wave lengths 
Tasriez I, 
7 € x! 
589°5 + 656°65 65656 +0-09 1600 52732 527°34 
612 + 652-07 652-25 —0-18 1645 523-69 523-71 
623 + 650°03 660°14 —0-1] 1708 518-79 518-79 
709 + 634-23 634-03 0-20 172 66 517-65 
172 + 62359 62339 +-0-20 2036 + 49611 496-05 
795 + 619°60 619:°90 —0-30 2 492-23 492°3 
813 + 617-48 617°39 +40-09 2 489°50 489-45 
818 ¢ 616-71 61671 0°00+40°18 2200 486-52 48652 0-00 +0-04 
813 + 61748 617-42 +0-06 2147 48950 48951 —0-01 
818 + 616-71 616-76 -0-05 2172 + 488-18 48811 +0-07 
843 + 612-75 61281 —0-06 ne 2 48659 —0-07 
856 + 610°80 610-73 +0-07 2236 + 48463 484° —001 
939 + 598-12 598-13 —0-01 2315 + 480°56 480°55 +0°01 +004 
1000 + 590°07 590-06 +0-01 9936+ 484-63. 46491 oes 
1005 + 58943 589-45 —0-02 + 0-04 2 an 
= 2315 + 480°56 480°26 +0°30 
1000 = 590-04 590°04 ~— 0-00 2785 «=6457°75 =9457°74 +0°01 
1005 = 89-43 689-45 ~—0-02 3272 440°81 440-33 +0-02 
1236 561°99 562:00 —0-01 3341 43863 438-67 -0- 
1247 560°70 560°65 +4-0-05 3597 431-°03 431:04 —0-01 £018 
1251 560-26 §60°22 +.0-04 : 
ioe ee sat ees 438-69 co08 
1413 + 543: . : ra 
PPAR ET, 64930. 4-007 £0 06 3532 432-78 432-81 —0-03 
1413 ¢ 54337 54344 —0-07 3597 431°03 431:00 0-03 
1422 542-33 542-91 —0-08 3728 427-45 42746 —001 
1445 ie 54109 —0-14 3773. 42626 426-28 —0-02 +004 
148] + 537-55 637-42 +10-13 
153 533°16 533°18 2 aes 3597 43103 430°97 +0°06 
1545 532-00 ee —O-01 3728 427-45 427°45 0-00 
15383 528-73 528-6 : 3773 §=42626 426:29 —0-03 
a +0-04 ; : 
1600 527-32 527-25 +0-07 ee eat eee 
4267 414°71 Hae Beh 
*, 0 . is 
4st 406-59 406-61 0-12-4006 
The method of interpolation employed was that first given 
by Cauchy* and afterward reduced to a practical form by M. 
Yvon Villarceau, in the Connaissance des Temps for 1852. 
in my recent Geet of Kirchhoff’s scale, I employed 
only expressions of the f 
has igs i é&e. 
these being found to to give an he ge ange within the limits 
of the Probable errors of observ 
able IT, gives the values of is “constants, a, b, ¢, and d, 
as deduced ion the data given in Table I. 
In this table H is the initi tial and H’ the terminal point of Mr. 
Huggins’s scale in each group of data employed for discussio® 
For easy use in calculation it is is more convenient to transfer #2 
_ and Secon points, so as to make each parabolic curv 
Caleul Differentiel t de Calcul Integral. Tome I*, 513. 
5 rein tocmck Two 1868, vol. xly, ia 
