There is nothing novel in any of these methods, and there is no doubt that other formulæ would be as good; but the one thing essential is to have a developer whose action can be held under control, and to apply that developer in such a way that very considerable over-exposure will not result in the ruin of the plate. If a number of photographs have been taken in about the same part of the sky, and within a short time of each other, then the correct proportions of developer and alkali will be nearly the same for all, but the first of such a batch will always have to be attacked in the cautious step-by-step method. Patience and perseverance, backed by a steady refusal to be discouraged by the failures which are at first inevitable, are as certain to be crowned by success as they are in other studies.
The workers are few, and there is much to be done; for it is mainly to those who will photograph the higher clouds, and so trace the stages of their growth and decay, that we must look for the data which will enable us to solve the problems they present, and so enlarge the narrow boundaries of our knowledge of some of the most beautiful things in Nature.
REFERENCES
1. “International Atlas of Clouds” (Atlas International des Nuages). Hildebrandsson, Riggenbach, and Teisserenc de Bort. Paris. 1896.
This is the atlas referred to in the text. The letter-press is short, and is repeated in English, French, and German.
2. “Annals of the Astronomical Observatory of Harvard College.” Vol. XXX. Observations made at the Blue Hill Meteorological Observatory. Part III. Measurement of Cloud Heights and Velocities. By H. H. Clayton and S. P. Fergusson. Part IV. Discussion of the Cloud Observations. By H. H. Clayton.
This last gives a very concise account of all the different proposals which have been made for the systematic naming of clouds.
3. “Études International des Nuages.” 1896-1897. Observations et Mesures de la Suède. I., II. Publication de l’Observatoire Météorologique de l’Université Roy. d’Upsala. H. H. Hildebrandsson.
An account of the Upsala observations referred to in the text.