THE AETIFICIAL INCUBATION OF OVA. 49 



as a float, to the top of which a fine hut strong chain 

 was soldered. The other end of the chain ter- 

 minated in a flat, round lump of lead. Pixed on the 

 top edge of the cistern was a freely-working grooved 

 transverse wheel acting like a pulley. The chain 

 hung over this groove, the box being inside floating 

 in the water, and the lead outside hanging upon the 

 upright scale, the chain being just long enough to 

 allow the box to sink to the bottom. The box being 

 heavier than the lead fell with the water, and as it 

 feU the lead rose; when the water rose the box floated 

 and the lead fell, the scale outside being calculated 

 to show the depth of water inside. I have found 

 this answer admirably, as it reported most accurately 

 and never got out of order for eight or nine months 

 together. The pisciculturist, however, must see that 

 the chain be suitably strong and does not open at the 

 links by use, or it may stretch and deceive hiim ; this, 

 however, would not makp an inch difference even at 

 the worst, 



- Before commencing operations see that the cistern 

 and its supports be thoroughly tested, and every ex- 

 periment that it may be desirable to make be made 

 in good time, as none can be made and nothing dis- 

 turbed when once operations are commenced. The 

 ■foundation supporting the cistern should be even 



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