ON THE MEASUREMENTS OF WAVE-LENGTHS. 
87 
The subjoined lists give the numbers of some of the lines of tin, lead, indium, and 
copper that occur between the cadmium lines 11 and 12, and near the cadmium line 
18. Each of these lines occurs therefore on two different plates, and has been twice 
measured. 
Some Lines of Tin, Lead, Indium, and Copper, of which duplicate measurements 
have been made. 
Copper. 
Tin. 
Plate 6-12. 
Plate 11-18. 
Plate 17-26. 
Plate 6-12. 
Plate 11-18. 
Plate 17-26. 
r 
3306-8 
3307 
2544-5 
2544-6 
3329-9 
3329-6 
2705-6 
2705-9 
3289-9 
3289-9 
2528-8 
2528*9 
3282-9 
3282-9 
2664-6 
2665-2 
3282-2 
3282-1 
2526-1 
2526-3 
3261-7 
3261-5 
2660-2 
2660-6 
3273*3 
3273-2 
2522-6 
2522-7 
3174-3 
3174-1 
2657-8 
2658-1 
3246-8 
3246-9 
2506-3 
2506-2 
2645-2 
2645-7 
2491-1 
2491-7 
2643-0 
2643-3 
2489*3 
2489-0 
2631-4 
2631-5 
2485-5 
2485-7 
2617-9 
2617-8 
2481-8 
2481-9 
2593-4 
2593-9 
2477-9 
2478-5 
2570*6 
2570-5 
2468-1 
2468-7 
2545-5 
2545-7 
2488-1 
2488-8 
2482-8 
2482-9 
Lead. 
Indium. 
Plate 6-12. 
Plate 11-18. 
Plate 17-26. 
Plate 6-12. 
Plate 11-18. 
Plate 17-26. 
r 
3277-9 
3277-5 
2716 
2716-7 
3236-5 
3236-0 
2713 
2712-9 
3242-4 
3242-4 
2697-8 
2697-7 
3246-5 
3245-7 
2709-1 
2709-5 
2662-4 
2662-6 
3255-3 
3255-8 
2706-0 
2707-0 
2650-0 
2650-0 
3257-7 
3257*9 
2630-6 
2631-7 
2627-1 
2627-8 
3273-8 
3274-0 
2600-3 
2600-3 
2613-2 
2613*5 
2559-6 
2559-4 
2576-3 
2576-5 
2553-9 
2554-3 
2566-8 
2567-6 
2527-2 
2527-0 
2561-3 
2561*8 
2475-5 
2476-0 
There is no distinction made in these tables between strong and weak or sharp 
and diffuse lines, and the numbers therefore represent the degree of accuracy common 
to our measurements of lines of different characters. 
Determination of wave-lengths from prismatic spectra .—Owing to the large portion 
of the spectrum being focussed on one plate, and the very fine definition of the lines, 
it was advantageous to take measurements from grating spectra, and determine the 
wave-lengths by interpolation between the fiducial lines. Faint lines, and some of 
the weak ones that were indistinguishable under the microscope, were marked by a 
fine needle-point, and a drawing of the line and point, as seen under a hand lens, was 
