IN PRACTICAL ASTRONOMY, SPECTROSCOPICALLY EXAMINED. 807 


ONE RUBY-RED GLASS INTERCEPTS. 


















Intensity, ‘ Wave-number| Colour Region by 
Max. = 10, 5 in Brit. inch. | Wave-number. 
False red glare at least as far. : ; 0-4 24500 | 23 585 | Ultra Red 
First supposed true ight . , ; ‘ 0-4 24670 | 26 882 | Ultra Red 
More certain ight . ‘ . ; ‘ 0-7 24:925 | 30 864 | Crimson Red 
Quite certain light. , ; ; ‘ 15 25°070 | 33 003 | Crimson Red 
Strong true red light . SMBS 2-7 25175 | 34 843 | Crimson Red 
Maximum Licur : : ; ‘ : 8:2 25°710 | 41 667 | Amber 
Yellow light begins . 4 : ; ; 8-0 25°765 | 42 194 | Amber 
Green light begins ‘ ; é ; C2 25°855 | 43 197 | YELLow 
Greenish black dark band . . i : 2:2 25°930 | 44 053 | YELLow 
Black reaches a maximum : : 0-7 25:975 | 44 563 | YELLow 
Black ends, and green band begins : ; 0:8 26155 | 46 189 | Crrron 
Green band ends, and false violet, caused 
by red glare, begins 5 : : : 15 26°550 | 49 826 | GREEN 
End of all light . ; ; : : : 0:0 27°385 | 56 101 | BLUE 
TWO RUBY-RED GLASSES INTERCEPT. 
False glare begins”. : ’ i 0-1 24550 | 24 814 | Ultra Red 
First true red light . : : : ‘ O-1 24803 | 28 986 | Ultra Red 
Decided red light ; : ; 14 25°070 | 32 895 | Crimson Red 
Strong red light te ; : ¢ 4:2 25°220 | 35 714 | Rep 
Maximum LIGHT : ; ; : : 71 25575 | 40 193 | Amber 
Green-black begins . : 2 ; 57 25°780 | 42 373 | Amber 
End of all true ‘spectrum light ; : . 0:0 25°880 | 43 459 | YELLow 
Red false glare faintly begins ; : 0-1 26:040 | 45 147 | Crrron 
Red false faint glare ends . : . : 0:0 26590 | 50 163 | GLaucous 
FOUR RUBY-RED GLASSES INTERCEPT. 
Red light begins at. ; : : : O-1 25°015 | 32 206 | Crimson Red 
Red light decided at . ’ ; ; ; 03 25:080 | 33 113 | Crimson Red 
Very decided . : ‘ : : : 1:2 25:170 | &+ 722 | Crimson Red 
Full red light. : : ; , : 24 25°23( | 35 842 | Red 
Maximum Licut ; . f , ; 45 25:50U | SS 370 | Orange 
Black shade begins. ; : : : 3:0 25°677 | 41 237 | AMBER 
Alllight ends . ; ‘ ; : ' 0:0 25°770.| 42 194 | AMBER 




Eight ruby-red glasses transmit a similar beam of red light, a little narrower, and more 
removed toward the ultra red, or at 37,820 wave-number. 
These ruby-red glasses are therefore eminent for transmitting one colour, and stopping all 
others. And further, the colour they transmit with every increased thickness of the glass is 
less refrangible than before. Hence, while with one thickness, and even two, there is much 
orange and yellow light transmitted close up to D, there is only, with five thicknesses, a red 
band near the place ‘of C. So very nearly indeed over it, that such glass may be usefully 
employed, perhaps, to facilitate solar prominence observations, 
The plates of glass employed above were white glass, flashed only on the surface with the 
ruby material, and “that often wavy and with strize like horse hairs, Enquiry should be made 
if such glass can be had of pot-metal and good in optical quality. Two opticians have obligingly 
undertaken to furnish me with such sun-shades, but when their work arrived it was found 
not to be exactly the ruby-glass tint, nor so clear a colour. 
