the other, the two ends being attached to a powerful cross bar, to which
is connected the lifting hook. By this means the weight is distributed
over the two sheaves and the two parts of the chain, increasing the
safety and diminishing the friction of the block.

"The blocks are very simple in construction, and are not at all liable
to get out of order; the construction being such that the weight cannot
run down, though the men lifting let go the chain. They hang quite plumb
when in action, and the men are able to stand clear away from under the
load, as the hand-wheel chain can be worked at any angle."

* * * * *




Plants In Sleeping Rooms.


The following from the able pen of Dr. J.C. Draper, in the January
number of the _Galaxy_, will answer some inquiries lately received on
the subject, and is a brief, but clear exposition of the injurious
effects of plants in sleeping apartments:

"Though the air is dependent for the renewal of its oxygen on the action
of the green leaves of plants, it must not be forgotten that it is only
in the presence and under the stimulus of light that these organisms
decompose carbonic acid. All plants, irrespective of their kind or
nature, absorb oxygen and exhale carbonic acid in the dark. The quantity
of noxious gas thus eliminated is, however, exceedingly small when