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and the condensers almost above it thus producing a greatly fore-shortened image of the whole mantle and utilising practically all the light emitted.
This apparatus ran for three years, with occasional patching up. I then decided partly from reasons of enforced economy and partly to minimise vibration, to build a motor which would run on two volts. This was successful except in the matter of the clock, the raising of whose weight in the short period available absorbed an undue amount of power. The perpetual motion idea was therefore sacrificed and the device constructed which I still use on all types of machine.
A 36-hour clock movement has, upon its minute hand spindle a light disc carrying from 1 to 36 gramophone needles. Within the range of these needles a flat spring projects, with a small mercury contact beneath. As each needle comes round it depresses the spring slightly and at this position makes contact with the mercury. The motor starting up performs the same operations as before and in addition draws the spring from under the needle and then allows it to return, this time of course just above the needle. Should anything fail to work and the spring be not drawn from the needle it is forced down upon a second mercury contact which rings a bell and efficiently alarms the establishment. Provided, therefore, that one winds the clock daily the machine can be relied upon to operate efficientlv or, failing this for any reason, promptly notify its inability to function.
With this contrivance available, and the experience resulting from countless failures, it seemed reasonable to predict that the ambition of many years was approaching realisation — the possibility of photographing, in accelerated movement the complete life — history of a plant, from the seed, through all its stages to the production of seed again. Unfortunately, the need for economy which had suggested the reduction of 4 volts to 2 volts now became so acute that it necessitated a further reduction of 2 volts to nil. The only business firm which had taken a practical interest in my experiments came, abruptly, to an untimely end, and my beloved machines, enveloped in dust excluding covers, stood here and there the personification of blighted hope.
Several years later I chanced to meet my friend the late John Avery and with his characteristic kindness he put me in communication with Mr. Harry Bruce Woolfe, and to the unfailing enthusiasm of this gentleman, which I gratefully acknowledge, and the practical support of his colleagues of British Instructional Films Ltd, I entirely owe the facilities which have enabled me to place on the screen not only the life-history of a single plant but a series of such films both of botanical interest and economic importance, carried out under conditions approximating very closely to those of the plant in the natural state, and including many phases, such as the underground growth, which could not possibly be observed in the usual manner.