[6] Nernst lamps are the best to use, as they produce abundantly the blue and violet rays which have the greatest chemical effect upon a photographic film. Carbon filament lamps are very poor in this respect.
[7] A description of the apparatus required will be found in Ganot's Physics.
[8] Great care must be exercised in using this solution, as it is exceedingly poisonous.
[9] Two clocks would isochronise if their hands travelled at precisely the same rate round the dials, but would not synchronise unless they both registered the same time as well.
[10] Line screens can be obtained from Messrs. Penrose, 109 Farringdon Street, London; or Messrs. Fallowfield, 146 Charing Cross Road, London.