362 
ME. WAEEEN DE LA EUE ON THE 
height, depicted in the eastern quadrant of fig. 1, Plate VI., is almost entirely covered in 
fig. 2, and that the difiere^ce of position of the moon in the two pictures, when measured 
by a suitable scale, indicates a motion of about 50" in the interval of two minutes which 
they include, — a result very near to the truth, for the actual progression in that period 
was 54"‘5. The photographs, however, as will be hereafter seen, are so much better- 
adapted for such determinations as these, that it is not worth while to dwell more upon 
the conclusions to be derived from the hand drawings. 
In the two coloured drawings. Plates VII. and VIII., I have depicted the result of 
my telescopic observations ; to facilitate my doing which at some future convenient time. 
I made a coloured sketch on the afternoon of the eclipse. This coloured sketch, the 
black-and-white drawings made at the telescope and shown in fac-simile in Plate VI., 
together with my photographs, which I have not hesitated to use to correct any errors 
of position or dimension in the sketches, have enabled me to give in these drawings what 
I believe to be a very truthful representation of the appearance of the prominences, 
immediately after the commencement and just before the end of totality. The corona 
I do not give as an absolutely true representation of that phenomenon, but as fairly 
resembling its general appearance. It has been derived from the photographs, so far as 
they show it. 
II. Account of the Photographic Observations. 
The Kew heliograph, with which the photographs were obtained, is represented in 
the accompanying engraving *. It was devised by myself, for the special object of 
making photographs of the sun’s disk, at the request of the Council of the Poyal 
Society, in accordance with a recommendation to that efiect by Sir John Herschel. 
It has an equatorial mounting of the ordinary form, after the so-called German 
model, to which is attached a clock-work driver. The tube is square in section, and 
larger at the lower end than at the upper or object-glass end. The object-glass has 
3-4 inches’ clear aperture and 50 inches’ focal length ; the primary focal image of the 
sun at his mean distance is 0-466 inch in diameter ; but before it is allowed to fail on 
the sensitive plate, it is enlarged to about 3-8 inches by means of an ordinary Huyghe- 
nian eyepiece. In the plane of the focus of the posterior lens of this eyepiece are 
attached two position-wires, which cross at right angles, and which were adjusted, 
approximately, into a position at an angle of 45° to a parallel of declination. The 
object-glass is so constructed as to ensure the coincidence of the chemical and visual 
foci; but this coincidence being somewhat disturbed by the Huyghenian secondary 
magnifier, the amount of adjustment required to effectuate the best chemical focus was 
ascertained very carefully by a series of experiments. 
* The engraving was copied from a photograph taken at Eivabellosa. The front boards of the observatory 
were taken out in order that this might be done. Mr. DowieES, who was charged with the prepai-ation ol 
the plates, is standing in the doorway leading to the developing room. Mr. Eetnolbs has a plate-holder 
ready to place in the heliograph, and Mr. Becklet is observing the time with the chronometer. 
