392 SCIENTIFIC RECORD FOR 1883. 



■extremity of the island the length of total eclipse is about five seconds 

 less. In Carriacou, the £)rincipal island in the Grenadines, the dura- 

 tion of totality is 3 m 21 8 ; at the northern point of Tobago it is l m 51 8 . — 

 ^Nature.) 



Photographing the corona without an eclipse. — In a paper read before 

 the British Association, Dr. Hugging gives an account of his more 

 iiecent experiments iu coronal photography. The photographs referred 

 to in his first paper read before the Koyal Society, 1882, December 21, 

 were obtained with a Newtonian reflector by Short. Since then Miss 

 Lassell has lent Dr. Hug-gins a seven-foot Newtonian telescope made by 

 the late Mr. Lassell. No secondary reflector is used, nor is the mirror 

 tilted, but the open end of the tube is fitted with a mahogany cover in 

 which are two circular holes three and a quarter inches in diameter. 

 Through one of these the light is admitted, and the framework for 

 carrying the sensitive plates is fitted over the other. The performance 

 of the apparatus is very satisfactory. The photographs show the sun's 

 image sharply defined, but it is only when the sky becomes clear and 

 blue in color that any coronal appearances present themselves. 



In Dr. Huggius's earlier work he employed absorbing media in order 

 to limit the light used to the violet rays. But much difficulty was ex- 

 perienced from the rapid manner in which the colored solutions (po- 

 tassic permanganate, or iodine in carbon disulphide) decomposed under 

 the influence of sunlight. Dr. Huggius therefore tried chloride-of-silver 

 plates, which are strongly sensitive to light between H and h, but 

 hardly at all beyond R, and has been able to secure photographs of the 

 corona with them, without the use of any absorbing medium at all. The 

 developer employed has been a solution of ferrous citro-oxalate, and 

 all the plates have been backed with a solution of asphaltum in benzole. 

 For the purpose of screening the sensitive surface from the intensely 

 bright image of the sun, small circular disks of thin brass, slightly larger 

 in diameter than the sun's image, were held close before the sensitive 

 plate. Less advantage was, however, found from the use of the disk 

 than had been anticipated. No photographs could be secured on May 

 6, the day of the total solar eclipse. One of the English observers of 

 the eclipse, however, having made a careful comparison of the short- 

 exposure photographs taken at Caroline Island, with Dr. Huggins's 

 photographs, expresses his opinion that Dr. Huggins's photographs 

 of the corona are certainly genuine up to 8' from the sun's limb. — {The 

 Observatory, November, 1883.) 



A private letter from Dr. Huggins, dated December 22, 1883, states 

 that "the solar photographs are now strengthened by a new process 

 which makes the fainter details more visible. A selection of plates has 

 has been sent to Mr. Wesley to draw from, and his drawings have been 

 compared with the negatives by Captain Abney. Of one of the plates 

 taken May 31, 18S3 (about one solar rotation period after the eclipse of 

 May 6), Mr. Wesley and Captain Abney independently made drawings. 



