Ohituary Notices. 
Ixxiii 
irom 3 to 15 miles. Accordingly, it became an object of import- 
ance to distribute the light supplied by an ordinary Fresnel’s 
second-order fixed apparatus, in the various directions in which it 
was to be viewed in quantity in some measure proportional to the 
distance it would have to travel to reach the observer’s eye, and 
this was effected by subjecting portions of the light not otherwise 
usefully available to the action of condensing prisms {Lighthouse 
Illumination, pp. 112-116). The late Mr James Melville Balfour, 
in reporting on the first trial of this light (October 1857), says, 
“ The prisms throw a light down Sleat Sound superior to any first- 
class light in the Northern Light’s service, and the light up Glenelg 
Bay is little, if at all, inferior in power ” (op. dt., p. 116). 
Here it falls to be recorded that Mr J. M. Balfour not only had the 
charge of the erection of the Isle Oronsay Light, but to him also 
was committed the working out of the necessary drawings and cal- 
culations required in designing it. In this work he obtained invalu- 
able, it might indeed be almost said essential, help from a recent 
ingenious invention of his own. This was his “ Optical Protractor,” 
the first instrument, I believe, of its kind (described in the Tran- 
sactions of the Royal Scottish Society of Arts, vol. v.),"^ 
And here seems a fitting opportunity for remarking how fortunate, 
in carrying out the application of his new lighthouse agents to actual 
lighthouse construction, Mr Stevenson was in possessing in the 
firm’s office two such coadjutors as Mr J. M. Balfour and Mr Alan 
Brebner. The latter, who became a partner in the firm of, D. & T. 
Stevenson, C.E., and died in 1890, was the inventor of a new 
optical protractor differing from Mr Balfour’s. During a period of 
many years he, along with other assistants in the office, executed 
the designs for the lighthouses constructed by the firm. Of the 
value of their co-operation in the work it is impossible to speak too 
highly. 
There still remain unmentioned many of Mr Stevenson’s light- 
house inventions, which, being not gmrely optical, have not been 
included in the preceding enumeration, but space can only now be 
* I have elsewhere (in my paper “ On New Forms of Lighthouse Apparatus,” 
Trans. Roy. Scot. Soc. Arts) expressed my extreme obligation to Mr Balfour 
for the invaluable aid I had obtained from the use of his ingenious instrument, 
without whose help I should scarcely have undertaken to protract the designs 
contained in my paper. 
