VENTILATING APPARATUS. 
29 
between two and three thousand cubic feet. The air in 
passing over chemical and other substances placed in 
this, was supposed to be deprived of its impurities, and 
in a great degree of its noxious properties. 
In the ‘ Wilberforce,’ however, it was found that a 
sufficient supply of air was not to be had by using the 
“plenum impulse,^’ or sending in fresh air. The con- 
trary or “ vacuum,” was therefore generally employed, 
to exhaust the foul air from all the remote recesses and 
stagnant corners of the ship. By these means what- 
ever action took place, was certainly beneficial ; whereas 
the “pZenwm”had no appreciable effect. Indeed the 
whole benefit — although the system was good in theory 
— bore no proportion to the disadvantage of occupying 
so much valuable space, or the still greater evil of 
detention in the preparation of the apparatus. 
It is, however, easy to pronounce judgment after 
experience has been gained. The greatest praise and 
most grateful acknowledgements are due to the talented 
inventor, for the zeal and solicitude he displayed in try ing 
to avert, by every means that science could devise, the 
baneful effects of the climate which too surely awaited 
us. The eiTor was in proposing to dole out the “pa- 
bulum vitoe” by two small apertures to so many gasping 
throats, for whom the hatchways are not large enough 
in a hot climate. 
Even in timber-built ships, there is always a con- 
siderable amount of deviation in the steering compasses, 
caused by the attraction of the large quantity of iron 
