THE AKTIFICIAL INCUBATION OF OVA. 39 



fuHy described presently, so that the attendant may 

 see at a glance how much water is in the cistern. 

 In turning the water into the trays, it must always 

 be held in mind that when the cistern is full the 

 weight of water drives the stream much faster 

 through the supply tap than when it is low. To 

 keep up an equable flow is therefore somewhat diffi- 

 cult, as in order to do so it is necessary to open the 

 tap slightly, more and more from time to time as 

 the water gets lower. The only way of reduciog 

 this to a certainty, and so being tolerably sure that 

 you do not run more than your proper calculated 

 allowance ?iway, is to have a tap which turns by 

 means of a straight handle or key (like those under 

 kitchen boilers) ; under this key fix a semicircular 

 plate with the degrees marked on, somewhat like 

 to the compass card. Then, having filled your cistern, 

 you can experimentalise upon the flow of water, 

 comparing the quantity run away in such and such 

 a time by means of the graduated scale against the 

 angle yoxi have set the key of your tap to on the 

 plate; by this means, after a few experiments, the 

 matter can be reduced to a tolerable certainty. 

 Having arrived at this, draw up a regular code of 

 instructions for the management of the cistern, and 

 see that whoever has the charge of it attends to 



