My Dear Sir,—Mr. Burnham is undoubtedly “facile princeps,” as an observer of double stars. Few men could have discovered such difficult objects as he has done with a 6″ O.G. Perhaps, it ought to be conceded that the usual formula for separating power, requires modification in his case, as Pogson’s formula for “minima visible” did with Mr. J. W. Ward, of Belfast. Apropos of this topic: do you recollect Mr. Ward’s discovery of several additional comites to Pxx 452 Cygni? One of them Mr. Burnham only succeeded in seeing with the greatest difficulty with the 6″ O.G. when the large star was hidden by a bar. I can see this easily enough with the 11-1/4 in. mirror, in presence of the brighter star.
When you have any intending customers halting between two opinions, or in any way dubious about reflectors—if you will refer them to me, I shall have great pleasure in giving my testimony. Reflectors have been very badly used, and in justice to them I shall not hesitate to express my honest conviction whenever it is asked.
Yours sincerely,
(Signed.)
Mr. G. Calver.
From Philip Vallance, Esq.
Cobb Court,
August 24th, 1880.
Dear Mr. Calver,—I write to thank you for the very excellent 12 in. mirror you have worked for me. You know that I have excellent opportunities of testing it by those of With, Bird, Grubb, Murrell, and others; and also for definition by a capital 6 in. refractor—and I can truly say it is surpassed by none, and equalled by few: it is quite my favourite instrument, and has been a source of much enjoyment ever since I have had it, and again I thank you for working me such a treasure.