DR. J. YOUNG AND PROFESSOR G. FORBES ON THE 
face of the hill was partially excavated, and two holes were “ jumped ” in a massive 
stone, in which two Y's were fixed to support the reflecting collimator. The reflector 
A was 8§ inches further from Kelly than the most westerly of these two holes. 
The reflector A was frequently shifted in direction (not in absolute position) by the 
unsatisfactory condition of the soil. This was especially the case during the severe 
frost of the winter, and on the occasion of the subsequent thaw. It was covered by a 
wooden box, open to the east. 
The reflector A was not interfered with by any inquisitive persons. But the box 
covering B was once broken open at the west end, and the centreing screws 
abstracted, doubtless with the aim of obtaining a view of Kelly House with what 
was supposed to be a powerful telescope. 
We made some sketches, and took some photographs of the apparatus, from which 
the accompanying plates have been prepared. 
\_Note. —It has been decided that the descriptions of the apparatus are sufficiently 
clear, and that it is unnecessary to supplement them by the plates to which allusion is 
here made.] 
The general arrangement of our apparatus gave us considerable satisfaction. We 
could have wished, however, to have had a chronograph of the same kind, but more 
convenient in use in some ways, with greater rigidity, and with a smaller moment of 
momentum about the axis. The mechanism of the toothed wheel might perhaps be 
constructed so as to give a greater velocity than we were able to obtain. If a better 
climate were experienced considerable advantage would be gained, and the telescope 
and reflectors might then be increased in size, and the distances lengthened.' 55 ' 
t [Measurement of the distances between the toothed wheel and the reflecting collimators . 
These measurements were made with the ordnance survey 20-inch theodolite. The 
base-line was the distance between the ordnance survey centre-marks on Knock Hill 
and Innellan Hill. The necessary information was furnished us by Colonel Clarke. 
It seems unnecessary to give details of the triangulation, the manuscript being left in 
the charge of the Boyal Society for reference. Calling Kelly House Station C, and 
the reflectors Stations A and B respectively, we obtained 
CA= 18,210*6 feet 
CB= 16,825*3 feet.] 
These distances require several corrections. 
* We wish to record our indebtedness during the whole series of the observations which follow, to 
the able and skilful assistance rendered to us by Mr. D. Stewaet, who superintended the working of the 
chronograph, and aided us in the work generally. 
f Details of triangulation have been left out. The part in square brackets here is substituted.— 
G. F., December 17, 1881. 
