Show abnormal twilights twilight which Is normally lite duo to the iho refraction of the suns light by tho the atmosphere Is occasionally by other natural causes rosy glows in tho the west after sunset aro are reported to lie bo par particularly ticul arty common in tho the vicinity of Dor dorveaux deaux france these arp aro not the flip usual sunset iset glows hut but appear in the pity 45 degrees above the sun and are arc supposed to he bo due to reflection from elgh clouds too thin to bo be seen in ordinary light tile the same clouds may also cause abnormal prolongation of twilight as on the first day of last july in this region where a watch could be easily read lead up tip to four min minutes ittes of 10 p ni whereas on tile the following night it could be read only a quarter past nine a difference of 41 mint minutes ites owing to the presence of the thin clouds above described these long twilights ard arc of uso use to 0 o astronomers astion as an all indication that the night will not be favorable for astronomical observation |