560 
MR. J. NORMAN LOCKYER ON THE 
forward to the eye end. The brass cap which protected the camera from light other 
than that which passed through the prism and object glass, is not shown in the 
diagram. The details of the attachment of the prism to the object glass cell is shown 
in fig. 2 ; provision is made for adjustment to minimum deviation and for rotating 
the prism and clamping it in any desired position, 
Details of prism mounting. 
The whole instrument worked very satisfactorily, except for a slight backlash in 
the driving screw, which could not be corrected. On a few of the plates there is 
evidence of a trail of the spectrum during the exposure, in consequence of this defect, 
and this trail seems to be partly answerable for the absence of some of the fainter 
details from some of the negatives. No trouble was experienced with the driving 
clock. 
The observatory provided for the instrument was 13 feet square, and 6 feet high, 
with a gable roof 4 feet in height. It consisted of a rough wooden framework, which 
had been completely prepared and marked before leaving England, covered with 
Willesden water-proof canvas. A portion of the covering of the roof was arranged 
so that it could be readily opened to admit of observations. The hut was very easily 
erected and it satisfied all requirements at a very small cost. 
