1878.] M. Janssen's JPTiotograpTis of tie Sun. 121 



In fact, an attentive examination of these photographs shows that the 

 photosphere is not of uniform constitution all over, but that it is divided 

 into a series of figures more or less distant one from the other, and showing 

 a distinct constitution. The outlines of these figures are generally rounded, 

 but often nearly rectilinear and resembling polygons. 



The dimensions of the figures are very variable. They sometimes 

 attain a diameter of one minute or more. Whilst in the intervals between 

 the figures, the grains are distinct and well-defined, although of variable 

 size, in the interior, they are half-effaced, drawn out and confused ; gene- 

 rally they have disappeared to give place to streams of matter which 

 replace the granulation. Every thing indicates that in these spaces, the 

 photospheric matter is undergoing violent movements which have confused 

 the granular elements. 



Another very important fact, shewn in a very certain manner by the 

 photographs, is, that numerous very dark points show themselves in the 

 parts where the granulation is regular, and indicate that the photospheric 

 layer must have a very slight thickness. 



Capt. Waterhouse remarked that some of the small photographs that 

 were' now being taken at the Surveyor- General's Oflice with the photo- 

 heliograph, frequently showed a mottling and figures of various shapes 

 that appeared to correspond with what M. Janssen called the photographic 

 net-work. These photographs were taken by Capt. Abney's beer-albumen 

 process, with alkaline development. Some photographs taken by Colonel 

 Tennant with the same instrument after the Transit of Venus showed 

 these figures very clearly indeed j they were taken by the ordinary wet- 

 collodion process, but were very carefully exposed and developed with 

 pyrogallic acid instead of iron. 



These photographs, on which the disc of the sun is only four inches, 

 are too small, and the definition of the instrument is not sufficiently good, 

 to permit of the details being enlarged, so as to make useful observations 

 of the daily state of the photosphere as M. Janssen was doing. For this 

 purpose, a much more powerful optical arrangement was necessary. 



The Eev. Fr. Lafont asked to what the distinct difference existing 

 between the various parts of the photograph exhibited was due, some parts 

 being very sharp in outline, others very ill-defined, as if out of focus. It 

 could not be that the tops of the flames in the chromosphere are sufficiently 

 distant from it to produce a difference of focus ; might it be that even in 

 the short duration of the exposure, these flames or some of them, displace 

 themselves enough to destroy the sharpness of their outlines ? or is it 

 due to some vibration of our own atmosphere ? He could hardly believe 

 that the movement of the protuberances is such as to sensibly displace them 

 upon the sensitive plate in the -^-^qq of a second. 



