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186 closely the substances with which they were dealing. At other times the masks hung at the girdles. At the fourth bed the workers wore the masks more frequently, and at the fifth they only removed them occasionally. The way of working at the sixth bed was different and will need a fuller description.

But before attempting to describe it I should say that just as I was beginning to observe the sixth bed, a slight change came in the weather which made two considerable changes, each in a different direction, in my opportunities of observation. It had been quite calm and at the same time cloudy. Now a light breeze began to blow and the sun shone out. The effect of the breeze was, at first, so to increase the motion of the car as to make very close observation impossible. But Signor Davelli presently applied a sort of ballasting machinery, which had the effect of greatly steadying the car. I was so much interested in what was going on below that I did not very accurately observe how this was done. But I think that it was somehow in this way. He moved, by mechanical contrivance, certain weights in the car, so as to change the centre of gravity in such manner as to render the part of it which we occupied subject to less motion than the rest. I have not much skill in such matters and I hardly