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15. Portable Ventilation Anemometer. (Fig. 17.)

In this small fan type of anemometer the registering apparatus is placed in a separate chamber on the same plane as the fan in order that there may be no obstruction to the passage of the air past the fan. The instrument records in metres the quantity of air that has passed through the fan. A table of corrections is always supplied with these instruments.

Fig. 17.

16. Eidograph. (Fig. 18.)

Although this instrument was invented by Prof. Willis so long ago as 1821, it is not extensively used. Its range of working power is somewhat limited, since it is not really effective for making a reduction beyond one-third of the original size. Within these limits, however, it reduces conveniently and exactly and in any proportion. The point of support is a pin supported by a heavy foot, the whole instrument being free to move round this pin. A socket which accurately fits the pin slides upon the centre beam of the instrument, at any part of which it can be clamped. Under the ends of the beam are placed a pair of equal wheels connected by two steel bands, the tension of which can be adjusted. Under each of these wheels is a box, through which one of the arms of the instrument slides and can be clamped where required. These arms are graduated, and one of them carries a tracing point and the other a pencil. The tracing point being moved over any drawing, the pencil point makes a copy of the drawing in the proportion for which the instrument has been set.

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Le texte affiché peut comporter un certain nombre d'erreurs. En effet, le mode texte de ce document a été généré de façon automatique par un programme de reconnaissance optique de caractères (OCR). Le taux de reconnaissance estimé pour cette page est de 99,54 %.

La langue de reconnaissance de l'OCR est l'Anglais.

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