1879.] CIRCULATION OF WATER IN PIPES. 569 



tainly were very effective. Another good feature in these beds was the un- 

 usually broad edgings of some, and the "inner edgings" of other beds. 

 Several good arrangements consisted as follows : centre, Mrs Pollock Pelar- 

 gonium, mixed with Viola Tory (a good purple), and broadly edged with 

 Coleus Verschaffeltii ; centre, a mixture of Pelargonium Crystal Palace Gem 

 and Viola Blue Perfection, broadly banded with Iresine Lindenii, edged with 

 Euonymus radicans variegatus ; centre, Pelargonium Eijou and Dactylis glo- 

 merata, broadly banded with Iresine Lindenii, edged with Stellaria graminea 

 aurea ; centre, Pelargonium Lucius, banded with two rows Abutilon vexilla- 

 rium variegata, edged with Alyssum saxatile variegata ; centre, a mixture of 

 Pelargonium Crystal Palace Gem and Viola Blue Perfection, banded by 

 Iresine Herbstii, edged with Symphoricarpus montana variegata ; centre, a 

 mixture of Pelargonium Bijou and Viola Favourite, broadly edged with 

 Coleus Verschaffeltii. The best bronze Zonal Pelargonium used was Black 

 Douglas, and Dr Denny's Commander-in-Chief was pointed out as being the 

 best and most enduring scarlet-flowering variety. "W. Iggulden. 



CIRCULATION OF WATER IN PIPES. 



The best way of making this subject clear is probably to resort to 

 facts which have been ascertained by experiment. The sole force 

 which operates to produce motion in the water is the force of gravity. 

 This force operates most strongly on bodies which are called the 

 heaviest, and by so operating it may even cause lighter bodies to rise. 

 Thus the light weight in the scale of a balance rises, because the 

 heavier weight in the other scale is more strongly acted upon by the 

 force of gravity. A cork rises from the bottom to the top of water 

 because a corresponding bulk of water is heavier — that is, is more 

 strongly acted upon by the force of gravity than the cork. Both cork 

 and water are pulled downwards, but the water (that fills the same 

 bulk) is pulled more strongly, and therefore the pull upon the water 

 overcomes the pull upon the cork — the water sinks, and the cork rises. 

 In precisely the same way if a portion of water is more dense — that is, 

 heavier than another portion — it will be pulled down, and the lighter 

 portions will be forced up by the heavier taking its place. Now, as 

 heat causes water to expand, or to become less dense, a given bulk of 

 cold water is heavier than the same bulk of warm water ; the cold 

 water is therefore pulled down, and forces the hot to rise. It is im- 

 portant to understand this, because people are apt to speak incorrectly 

 of heat causing water to rise. It does nothing of the sort. From 32° 

 to 39°. 2 the action of heat causes water to contract, or to become 

 heavier, and, therefore, if a portion of water is warmed to any degree 

 below 39°. 2, it will sink instead of rising in the midst of water — that 

 is, if a lower temperature. Above 39.2°, however, heat causes water 

 to expand or become lighter, and then it will rise, because the colder 

 and heavier water falls lowest and forces it up. 



2 Q 



