486 



HYDRODYNAMICS. 



lUdrosta- mouth of the stop-cock D is closed, and the air is drawn 



tical In- out O f the i on g er branch by suction at E. Instead of a 



Md EJW" st P- cock at B > tne finger may be applied till the air is 



rimenuT" <* ed out at E - 



14. Description of a Syphon acting by Capillary At- 

 traction. 



Description ^ * bunch of cotton or worsted threads, or any ab- 



of a syphon sorbing fibres, is placed with one extremity in a vessel 



actingbyca- of water, and with the other hanging over the edge of 



pilUry at- j t> t ] le fl u j c i w ;u r ; se arao ng the threads by the force f 



lon ' capillary attraction, and the water will be discharged 



from the longer branch in successive drops. Mr Leslie 



has very ingeniously employed this syphon for keeping 



moist the bulb of his hygrometer. 



15. Explanation of intermitting or reciprocating Springs 

 upon the principle of the Syphon. 



Kxplana- 

 tion of in- 

 tennitting 



springs up. 

 on the prin- 

 ciple of the 

 syphon. 



PHTK 

 CCCXVII. 

 Pig. 12, 



To eon- 



which the 



escape 

 when it 

 reaches a 

 certain 

 height. 

 Fig* 13* 



A reciprocating spring, is a spring which alternately 

 flows and ceases to flow. The name is also given to those 

 g p r i n g 8 w hich have a periodical swell, or which discharge 

 a g reat quantity of water at one time, and a small quan- 

 tity at another, after regular intervals. The first of 

 these kinds of springs is easily accounted for, by snp- 

 posing that the channel which carries off the water from 

 a cavern has the form of a syphon. In this case, the wa- 

 ter will only flow when it rises in the cavern to a height 

 equal to that of the syphon, and the flow will stop till the 

 cavern is again filled to the same height. The following 

 explanation of the second kind of intermitting springs 

 was suggested about a century ago to Dr Atwell of Ox- 

 ford, by the phenomena of Lay well Spring at Brixam, near 

 Torbay, in Devonshire. Let A A be a large cavern near 

 the top of a hill, which derives its supply of water from 

 rains or melted snow percolating through the chinks of 

 the mountain, and let CC be the small channel which 

 convey the waters of the cavern to the opening G in the 

 hill, where they are discharged in the form of a small 

 spring. From the cavern AA let there be a small channel 

 D, which carries water into another B, and let the water 

 of the second cavern be carried off by a bent channel E e F 

 wider than D, and joining the first channel CC at /, be- 

 fore it issues from the mountain, the point of junction 

 f being below the level of the bottom of both the ca- 

 verns. As the cavern B fills with water, the fluid will 

 ascend to the same height in the channel EeF, but it 

 will not be discharged by this channel till the surface 

 in B is on a level with e, the highest part of the chan- 

 nel. The water will then be carried off by the natural 

 syphon E e FG, till the whole is discharged, and conse- 

 quently there will be a great swell in the spring at G. 

 This swell will now cease, as the channel D does not 

 convey the water into B so fast as the syphon EeF 

 carries it off; and it will again commence as soon as the 

 water in B rises to a level with the summit e. Mr Fer- 

 guson has illustrated this operation by a simple machine, 

 a description of which will be found in his Lectures, 

 vol. ii. p. 106, 107. 



i6 ' To construct a Vessel, from tvhich the Water will 

 escape rehen it reaches a certain height. 



This vessel, which is called Tantalus's cup, consists 

 of a metallic vessel, ABCD, divided into two corn- 

 partments by the partition EF. A glass tube H /(, open 

 a t both ends, is inserted in the opening H, in the parti- 

 t j on gp^ tne i ower enr j being allowed to reach a little be- 





low EF. The tube H h must then be covered by a Hydrosta. 

 small glass receiver a b c, or a wide tube hermetically tical !" 

 sealed above, a small aperture being left at the bottom - strl en " 

 of this tube to admit the water. This mechanism is ^jmg^ 

 generally covered by the figure of a man representing --- ^ 

 Tantalus, as shewn in the drawing. If water is now FLATS 

 poured into the vessel, it will get admittance into the CUCXVII. 

 receiver or wide tube, and will always stand at the ^'&' ^ 

 same height in this tube that it does in the vessel. 

 The water will therefore be retained in the vessel as 

 long as it does not enter the tube H h, but as soon as 

 the water rises in the vessel to the same level as the 

 point h, it will flow down the tube H h ; which acting 

 like a syphon, will discharge the whole fluid in the ves- 

 sel. If water is poured slowly in with the intention of 

 making it rise to the lips of Tantalus, it will never 

 reach them provided the syphon carries off the water 

 faster than it is poured in. In the lower compartment 

 of the vessel, there ought to be a small air-hole near 

 the top, to allow the air to escape when the water takes 

 its place. 



17. To construct a vessel which retains water when it is 



upright, but discharges it when it is inclined. 



Let ABCD be the vessel divided as formerly into two T O con . 

 compartments by the partition EF. Into this partition struct a 

 insert the longer branch b c of a syphon a b c, whose vessel 

 shorter branch b a reaches nearly to the bottom of the which re- 

 vessel. If water is now poured into the vessel till it 

 stands a little below the lower side of the bent part of the u'p'ght.bo 

 syphon, it is obvious that no water will descend through discharges 

 the syphon, as it has not risen high enough through the it whcrTit 

 shorter branch to enable it to pass through the bent por- is inclined. 

 tion. If the vessel, however, is inclined to one side, as 

 it is in the act of drinking, the water will rise higher 

 in the short branch a b, pass over the bent part o 

 the syphon, descend in the longer branch, and carry off 

 all the water into the lower compartment of the vessel. 

 In order that this experiment may succeed, the sides of 

 the vessel ought not to be symmetrical round the point 

 a at the summit of the syphon ; for in this case no in- 

 clination of the vessel, however great, will cause the 

 water to flow over the point a. The syphon should 

 therefore be placed towards one side of the vessel, and 

 the vessel inclined to the same side. 



A similar effect may be produced much more ele- 

 gantly by using the double cup shewn in Fig. 1 5. where Fig. 13. 

 a b c represents the syphon. The person who tries to 

 drink, must apply his lips to the side b of the syphon, 

 otherwise the experiment will not succeed. 



18. To construct a machine in tvhich all the water pro- 

 jected into a basin from a jet d'eau appears to be drank 



by a bird. 



This ingenious and elegant machine is shewn in Fig. To con- 

 16. where ABCD is a vessel divided into three compart- struct a 

 ments by the partitions EF and GH. In the partition machine in 

 EF insert two tubes, one of which LM, forms a com- ^'* a ," r 

 munication between the bottom of the compartment pl . : ecte( i 

 BG and the bottom of EC; while the other tube IK forms j n tun basin 

 a communication between the upper part of EC and the from a 

 upper part of HF. A third tube NO is fixed in thejttd'eau 

 cover AB, extending from near the bottom of HF, and B PP* ar w 

 rising with a tapering bore to the point O, through the ^ ^'bird. 

 middle of the vessel SR, intended to receive the wa- . 

 ter which falls from the pipe NO. The figure of a * 

 bird with its bill immersed in the water in the basin SR, 





