James Timmins Chance to Faraday   2 January 1861

Hamstead Birmingham | 2 Jany: 1861

My dear Sir,

I wish you all the compliments of the New Year.

Concerning the Smalls Light:- I have only yesterday surmounted the various practical difficulties, of an unforeseen kind, which have developed themselves in the actually carrying into effect the new plan of adjusting the different members of a fixed light refractor.

I believe that the plan may now be said to be practically successful, so that workmen may be entrusted with the execution of it.

It has been impossible for me to say until now at what height in the apparatus the focal plane would most conveniently be placed, because that height depended partly on the altered breadths of the ribs below the middle belt. Before, therefore, I dare have one single reflector fixed, I was compelled to wait for the completion of a panel of refracting ribs.

Everything will now proceed uninterruptedly; and I am in great hopes that the whole apparatus will be ready for inspection by the 10th of January:- but as I do not feel perfectly certain of this, I should prefer your naming some day in the week after next week¹, if equally convenient to yourself;- and I shall feel obliged by your letting me know by the return of post what that day will be in order that I may keep myself disengaged.

I gave you some time ago an unfinished table of the dips for different heights of tower, prepared according to the suggestions of Captn. Ryder. In that table the angles were those at the sea:- and they had to be reduced by 1/7th to obtain the visible angles at the apparatus.

In the enclosed table the angles are the actual visible angles at the apparatus: and the correction for refraction adopted in the calculations is that which the Astronomer Royal has been kind enough recently to communicate to me.

For the ‘Smalls’ Light the dip is 10’ 54” (for 125 feet in height) and the corresponding quantity at the axis of the apparatus is nearly 3mm, as you have given to the Trinity Board.

The angle of divergence which illuminates from the sea-horizon up to the one mile distance from the tower is only (about) 1 degree.

Apart from the new arrangement of the foci of the fixed refractor, the plan of internal observation in the adjustment is a most important step in the Art of Dioptric Apparatus and is well worth all the trouble which it has involved.

Most truly yours | (signed) James T. Chance