OF THE VAPOURS OF BENZENE AND TPS HOMOLOGUES. 
483 
I. 
11. 
III. 
IV. 
V. 
VI. 
2695 
44 
2689 
— 
— 
— 
— 
2651 
43 
2687 
— 
— 
— 
29 
2646 
45 
2682 
— 
— 
2622 
29 
2642 
45 
2674 
— 
20 
2617 
26 
2637 
41 
2670 
2602 
18 
2616 
26 
2633 
39 
31 
2599 
22 
2611 
27 
2631 
2571 
31 
2594 
21 
2606 
27 
30 
2568 
36 
2590 
18 
2604 
2541 
38 
(2558)1 
■— 
(2588 )1 
— 
35 
2530 
37 
— 
35 
— 
(2506)1 
38 
(2521 )1 
-— 
2553 
— 
83 
2492 
40 
— 
— 
— 
(H2S) 1 
75 
(2481 )1 
-—■ 
— 
— 
48 
2417 
70 
2471 
— 
— 
2375 
58 
2411 
63 
— 
— 
— 
2359 
58 
2408 
— 
— 
— 
- f 
2353 
59 
2397 
— 
— 
— 
— 
2349 
— 
2391 
A regularity is apparent in the differences between the wave-lengths of the successive 
hands in the six different groups. 
On the Relationship between the Bands of Benzene and Toluene. 
It will be seen on comparing their measurements that, without being precisely 
similar, all the bands of toluene have corresponding bands in the benzene spectrum. 
Where the former are weak and the latter strong it might be supposed that a trace of 
benzene was contained in the toluene, but where both groups of bands are strong it is 
evident that they are common to both spectra, even when the bands show slight 
differences between the values of their wave-lengths. The principal difference lies in 
the most important groups of bands in the toluene spectrum being situated more in 
the direction of the red rays than the corresponding groups in benzene, but notwith¬ 
standing this shift of the bands to a less refrangible region which had long previously 
been observed in the spectra of solutions, a similarity in constitution is to be seen 
between certain groups of bands in toluene and others in benzene. Furthermore, both 
spectra have one very strong band in common; though this is best shown on the 
photographs, a tabulated statement of the measurements of the spectra also makes it 
apparent. The bands of toluene appear generally in pairs of similar intensity, while 
those of benzene are composed, as already stated, of one strong band and one slightly 
less strong. The pairs of the toluene bands diminish in intensity as they lie more 
towards the more refrangible rays, and if the individual narrow bands were brought 
closer together they would constitute a group scarcely distinguishable from one of the 
benzene groups. This suggests that the same vibratory motions are taking place 
3 q 2 
