1. “ Whether seeds, especially such as are of hasty growth, videlicet, 
orpin, lettice, garden-cress seeds, &c. will germinate and thrive in the ex¬ 
hausted receiver of an Air-Pump?” 
the pressure of the air, greatly engaged their attention, and many additions were made to their disco¬ 
veries. Mr. Boyle, the most ardent and successful studier of Nature, had the principal share in these 
improvements, his inquisitive mind being aided by an opulent fortune. In a letter to his nephew. 
Lord Dungarvon, he says, that he made many attempts to see the appearances exhibited by bodies freed 
from the pressure of the air. He had made Toricellian tubes, having a small vessel at top, into which 
he put some bodies before filling the tubes with mercury; so that when the tube was set upright, and 
the mercurv run out, the bodies were in vacuo. He had also abstracted the water from a vessel, with a 
small pump, by means of a weight, having previously put bodies into the vessel along with the water. 
But all these ways were very troublesome and imperfect. He was delighted when he heard from 
Schottus’s first publication, that Counsellor Guericke had effected this by the expansive power of the 
air; and immediately set about constructing a machine from his own ideas, no description of Guericke’s 
being then published. 
It consisted of a receiver, furnished with a stopcock and syringe, placed in a vertical position below 
the receiver. Its valve was in its bottom, close adjoining to the entry of the pipe of communication; 
and the hole by which the air issued was farther secured by a plug which could be removed. The pis¬ 
ton was moved by a wheel and rackwork. The receiver of Guericke’s pump was but ill adapted for 
any considerable variety of experiments; and accordingly very few were made in it. Mr. Boyle’s re¬ 
ceiver had a large opening, with a strong glass margin. To this was fitted a strong brass cap, pierced 
with a hole in its middle, to which was fitted a plug ground into it, and shaped like the key of a cock. 
The extremity of this key was furnished with a screw, to which could be affixed a hook, or a variety of 
pieces for supporting what was to be examined in the receiver, or for producing various motions within 
it, without admitting the air. This was farther guarded against by means of oil poured round the key, 
where it was retained by the hollow cup-like form of the cover. With all these precautions, however, 
Mr. Boyle ingenuously confesses, that it was but seldom, and with great difficulty, that he could pro¬ 
duce an extreme degree of rarefaction; and it appears by Guericke’s letter to Schottus, that in this respect 
the Magdeburgh machine had the advantage. But most of Boyle’s very interesting experiments did not 
require this extreme rarefraction; and the variety of them, and their philosophic importance, compen¬ 
sated for this defect, and soon eclipsed the fame of the inventor to such a degree, that the state ot air 
in the receiver was generally denominated the vacuum Boyleanum, and the air-pump was called 
machina Boyleana . 
He was soon assisted by Dr. Hooke, the most ingenious and inventive mechanic that the world has 
ever seen. This person made a great improvement on the air-pump, by applying two springes, whose 
piston-rods were worked by the same wheel, and putting valves in the pistons, in the same manner as 
in the piston of a common pump. This evidently doubled the expedition of the pump s operation: and 
it also greatly diminished the labour of pumping; for it must be observed, that the piston must be 
drawn up against the pressure of the external air, and when the rarefaction is nearly perfect, this re¬ 
quires a force of nearly fifteen pounds for every inch of the area of the piston. Now when one piston 
is at the bottom of the barrel, the other is at the top of the barrel, and the air below is equally rare 
with that in the receiver. Therefore the pressure of the external air on each of the pistons is nearly 
equal. Both, therefore, are acting in opposite directions on the wheel which gave them motion; and 
the force necessary for raising the piston is only the difference between the elasticity of the air in the 
two barrels. This is very small in the beginning of the stroke, but gradually increases as the piston 
descends, and becomes equal to the whole excess of the air’s pressure above the elasticity of the remain¬ 
ing air of the receiver when the air of the natural density begins to open the piston valves. An accu¬ 
rate attention to circumstances will shew us that the force requisite for working the pump is greatest 
at first, and gradually diminishes as the rarefraction advances; and when this is nearly complete, hardly 
any more force is required, than what is necessary for overcoming the friction of the pistons, except 
during the discharge of the air at the end of each stroke. This is then the form of the air-pump which 
is most generally used all over Europe. Encycloped. 
