484 



Lord Rayleigli on the Visihility 

 Table (continued). 



Weight. 



Wave-length. 



.Weight. 



Wave-length. 



Weight. 



Wave-length. 



7 



6924-422 



4 



7168-216 



4 



7318-807 



5 



6929-823 



5 



7176-365 



3 



7321-052 



7 



6947-777 



5 



7184-791 



3 



7331-204 



8 



6956-708 



5 



7186-570 



2 



7335-631 



7 



6959-715 



4 



7200-768 



5 



7446-017 



8 



6961-521 



4 



7201-487 



5 



7495-347 



4 



6978-657 



3 



7216-819 



o 



7511-272 



8 



6986-841 



4 



7223-927 



4 



7594-061 



5 



6989-254 



3 



7227-773 



S 



7621-268 



6 



6999-171 



3 



7232-512 



5 



7623-529 



4 



7006-166 



3 



7233-170 



5 



7624-852 



5 



7011-585 



4 



7240-964 



4 



7627-255 



6 



7016-701 



4 



7243-898 



4 



7628-528 



S 



7023-762 



2 



7247-467 



3 



7659-643 



s 



7027-727 



3 



7264-851 



3 



7660-763 



7 



7035-167 



3 



7265-832 



4 



7665-254 



5 



7038-479 



2 



7270-210 



4 



7666-236 



S 



7040-069 



4 



7273-246 



4 



7670-974 



4 



7090-686 



3 



7287-690 



4 



7671-977 



4 



7122-522 



4 



7290-707 



2 



7699-344 



4 



7147-958 



4 



7300-062 



2 



7714-657 



4 



7148-438 



4 



7304-468 







LVI. On the Visihility of Faint Interference-Bands, By 

 Lord Rayleigh, Sec. R.S., Professor of Natural Philo- 

 sophy in the Royal Institution^ . 



IN a recent paper on the limit to interference -when light 

 is radiated from moving molecules f, it was necessary to 

 form an estimate of the ratio of illuminations (Ji) at the darkest 

 and brightest parts of a system of bands corresponding to the 

 moment when they just cease to be visible from lack of con- 

 trast. In the comparison of uniformly illuminated sui'faces, 

 brought well into juxtaposition, h might be as great as '99^; 

 but in the case of bands, where the transition is gradual, a 

 higher degree of contrast between the brightest and darkest 

 parts may be expected to be necessary. In order to allow 

 for this, I supposed that h might be estimated at "95, the 

 intensity of the light and the angular magnitude of the bands 

 being assumed to be suitable. But since widely different 

 estimates have been put forward by others, I have thought it 



* Communicated by the Author, 



t PMl. Mag. April 1889. 



X See Helmholtz' ' Physiological Optics,' § 21. 



