182 



THE POPULAR EDUCATOR. 



turn to those whose axes are vertical. Some of these are now 

 coming into much more frequent use, being in many respects 

 superior to those we have been considering, as they utilise a 

 larger portion of the force, occupy less room, and work under 

 water. 



The meat useful and generally used of these is the turbine. 

 A cylinder is constructed with an opening round its lower 

 portion, through which the water is allowed to flow from the 

 higher to the lower level. Surrounding this opening, the width 

 of which can be altered at pleasure, is a horizontal wheel with 

 curved floats. This wheel is under water, and is supported by 

 , plate on which it rests, its axle passing up through the 



cylinder. The water as 

 it issues from the cylin- 

 der strikes against the 

 floats, and thus turns 

 the wheel with very 

 great speed. 



Perhaps tho best idea 

 we can form of it, with- 

 out actually seeing one 

 at work, is to imagine 

 a water-wheel with 

 curved floats to be 

 turned on its end, and 

 the internal cylinder 

 removed, leaving the 

 floats supported on the 

 lower end, and held in 

 their place above by a 

 Fig. 27. ring, to which they are 



fastened. The water is 



then allowed to flow into the interior of the wheel, and in its 

 rush to escape between the floats it strikes upon their curved 

 surfaces, and thus sets the wheel in motion. 



In order that the water, instead of flowing directly from the 

 centre, may strike tho floats at a more advantageous angle, the 

 cylinder is divided into compartments by means of curved par- 

 titions after the plan shown in Fig. 27, which represents a 

 horizontal section of the cylinder and wheel, the outer ring 

 being the wheel. By this it will be seen that the water issues 

 in a direction almost perpendicular to the siirface of the floats, 

 and thus produces the greatest effect. As the water enters at 

 the inner side of the wheel and is given off from the exterior, 

 there is little loss from currents in the water ; the pressure, too, 

 on the axle being equal in every direction, there is not a large 

 amount of friction as there is in water-wheels, where the pressure 

 acts only on one side. 



The mode of construction just explained gives the best idea 

 of the principles on which the turbine acts, but many important 

 alterations and modifications have been introduced which 

 render the machine more useful. In some, the water, instead 

 of issuing from the sides of the cylinder, flows from an opening, 

 or a series of openings, in the bottom on to a wheel whose floats 

 are curved vertically, the construction being then similar to 

 that shown in Fig. 28. A still further improvement on this 

 is effected by allowing the water to enter 

 from below instead of from above, as in 

 this way, instead of increasing the pres- 

 sure on the bearings, it in a great degree 

 removes it. As, however, all different 

 makers of turbines have special plans, 

 differing more or less, and we have 

 seen the general principle on which 

 all act, it is unnecessary to describe 

 minor details. 



Another wheel which is much used in 

 France is called the spoon wheel ; several 

 arms having somewhat of a spoon shape 



radiate from a centre to which they are fixed. These are so 

 inclined that when the water issues from the trough along 

 which it flows, it strikes them almost at right angles to their 

 surface, and hence imparts a rapid rotation to the wheel. 



There is another apparatus by which motion can be derived 

 from falling water, which is frequently exhibited as a lecture- 

 table experiment, but seldom, if ever, used in practice. It is 

 known by the name of Barker's Mill, or the Wheel of Eecoil, 

 .and is represented in Fig. 29. M is a glass vessel, mounted 



Fig. 28. 



so as to turn upon an axle, and capable of being filled by means 

 of a stopcock at the top. If used practically it would, of 

 course, be so shaped that the water 

 could enter here as rapidly as it 

 issued below. At the lower part two 

 arms, c c, are inserted. These are 

 turned round at the end as shown 

 at A, so that the water can issue 

 from them, and in so doing, by its 

 recoil, it causes the vessel M to rotate 

 on its axis. Every part of the inner 

 surface of the tube sustains a pres- 

 sure produced by the water in the 

 vessel, but the pressure on opposite 

 sides of the tube is equal, and there- 

 fore no motion ensues from it, the 

 opposite pressures neutralising each 

 other. As, however, a portion of the 

 surface is removed at A, the pressure 

 on the part opposite to it is not ba- 

 lanced, and therefore causes motion. 

 This mill is, however, at present only an ingenious scientific 

 toy, nor does there seem much probability of its ever coming 

 into use. 



Fig. 29, 



ANSWEKS TO EXAMPLES IN LESSON VI. (page 119). 



1 . The specific gravity of the silver is 10'359. 



2. 1-694. 



3. The elm weighs 69'896 oz. ; the limestone 276'042 ; and the lead 

 1182-292. 



4. The specific gravity of the oil is 0'916. 



5. The stone weighs in air 26 grains, and it loses lOi grains in 



26 



water. Its specific gravity is therefore r --=, or 2'476. 



lO'o 



6. The two together displace 6 '84 oz. of water; of this 1'92 oz. is 

 due to the metal ; the wood therefore displaces 4'92 oz., and its weight 

 is 3'3. Its specific gravity is therefore 0'670. 



7. The volume of any body is represented by its weight divided by 



48 

 its specific gravity. Hence the volume of the copper is , while th:it. 



27 75 



of the zinc is ^-i^. The volume of the compound is therefore 



7-191' 



48 27 7i 



Hence ~ + ^ = 



compound as nearly 8'2. 



sp. gr. 

 , and this gives the specific gravity of the 



LESSONS IN ITALIAN. XXV. 



WE shall now proceed to give the learner several exercises for 

 practice. 



VOCABULARY. 



Addormcntato, -a, 



sleep. 

 Afi'abile, nffable. 



Destra, right hand. 

 Di fuori, without, out 

 of doors. 



/immolate, -a, ill, un- ' Di sopra, up stairs, at 



the upper end or 



part, etc. 

 Fuori, out of. 

 La giii (laggiu), down 



there, below there. 

 La su (lossii), up there. 

 Pigro, -a, lazy. 

 SbalorcLito, -a, amazed, 



confounded. 



Scortese, impolite, dis- 

 courteous. 



Scttola, school. 



Sonnolento, sonnachio- 

 so, -a, sleepy. 



Sli'avagante, eccentric, 

 odd. 



Svegliato, -a, awake. 



Tauola, table. 



Teatro, theatre. 



Timido, -a, timid. 



Veccliio, -a, old. 



well. 



Batjno, bath. 



Capriccioso, -a, capri- 

 cious. 



Casa, house, home. 



Oliiesa, church. 



Circospetto, -a, wary, 

 cautious. 



Dentro, within. 



EXEKCISE 32. 



1. So-no es-si af-fa-bi-li ? 2. El-la non e ca-pric-cid-sa. 3. 

 I'-o e-ra sve-glia-to. 4. Noi e-re-va-mo sba-lor-di-ti. 5. E'-gli 

 fu di sd-pra. 6. E's-se so-no sta-te am-ma-la-te. 7. Voi e-ra- 

 va.-te sta-to in chie-sa. 8. Se-i tu vec-chio ? (vec-chia r). 9. 

 Non sia-mo noi cir-co-spet-ti ? 10. I'-o e-ra sta-to nel ba-gno. 

 11. E's-si sa-ran-no fxior di cit-ta. 12. So-no ei-se ti-mi-de ? 

 13. Voi sie-te pi-gri (pi-gre). 14. Non sie-te voi stra-va-gan-ti ? 

 15. E'l-la e-ra ad-dor-men-ta-ta. 16. E'-gli e sta-to in i-scuo-la. 

 17. I'-o sa-rd a ca-sa. 18. E'-gli non e scor-te-se. 19. Noi fum- 

 mo di fuo-ri. 20. E's-si so-no stii-ti at'i-vo-la. 21. Voi fd-ste 

 la giii (lag-giu). 22. E's-si fu-ro-no la su (las-su). 23. E'l-la 

 e sta-ta in tea-tro. 24. E'l-la fu di den-tro. 25. Noi sia-mo 

 sta-ti a de-stra. 26. Tu e-ri son-no-len-to (son-na-chid-so). 



* 



