Viewing page 86 of 140

This transcription has been completed. Contact us with corrections.

82.

[[image: drawing of a tall, U-shaped vessel A B C D with a nozzle or spout K at the bottom.  There are four horizontal lines across the vessel H I one-tenth of the way down, M N one-fifth of the way down, and 3/5ths of the way down.]]

But ye same thing doth not happen when ye pipe is but 1/2 foot large and 2 or 3 feet heigh as ye pipe A B C D having a hole K of 6 lines for ye swiftness of ye water wch descends while it runs out gives an impulse to that wch goeth out, wch joyned to ye weight of ye water makes it go swifter than it makes it when it descends slowly ye pipe being very large.  I have many times found that if ye water would run out entirely from such a reservatory in 4 minutes, that there would want 11/26 when it was kept full of going out in 2 minutes, and if that pipe might contain 24 pints and that they would run out in 4 minutes there would go out but 10 keeping it full in ye space of 2 minutes and 24 seconds:   That defect proceeds from hence that ye spout is more retarded by ye rubbing and by ye resistance of ye air in pro- when it is swift than when it is feeble as is explained above, and so it is always equally retarded by these 2 causes when ye pipe is maintained full;  but it is less when ye water is but at ye height L M, and yet less when it is descended to F G.  It is here that if ye water turns round as it sometimes happens then ye running out shall be retarded, and may recompense ye effect of ye acceleration:  This turning round is made when ye hole is not in ye same plane, and that ye running water goeth out a little across in one place

  In ye last experiment I made of this matter ye water was 10 inches heigh above a hole of 4 lines wch was fixed to ye inner bottom of ye vessel.  There was placed at ye side of ye hole at ye same height where were taken 20 inches wch were divided into 36 parts;  ye first from ye hole had one of those parts ye 2d 3, ye 3d 5, ye 4th & ye 5th 9 and ye 6th 11:  Ye first division from ye top run out in 30 seconds, ye two following ye same;  ye 4th employed 36 seconds and each of ye other yet less, althô ye water made then a turning round wch might arrive from the acceleration of ye water when it went thrô ye hole.  Ye same proportion is yet less observed when ye hole is very great is proportion of ye height, as if it hath its diameter equal to ye 4th or 5th part of that of ye base of ye cylinder A B D C:  For ye water will run in great abundance and by consequence will much accelerate its swiftness in descending and will shoc so strongly that wch goeth out that althô its weight is then less than when it was in A B ye impulse will surpass that default, and there will go out more water thrô ye hole K when ye upper surface shall be at H i or L M than when it was in A B.  This truth will be easily known if we consider that when ye pipe is all open, ye upper water descends in equal times according to ye odd numbers following 11, 7, 5: 5, 3, 1, &c and that when ye pipe is very long and ye hole very small it descends according to ye numbers 7, 9, 7, 5, 3, &c and it follows necessarily that we can proportion ye heights, ye widnesses and ye holes of ye pipes so as to temper ye swiftness as we please that is to say that we may make 2 halfs pass in 2 equall times, and that ye 3d part towards the base shall be void in a time 3 times less than ye rest, and so of ye other parts:  But when ye water shall be far descended as in F G, it will not any more accelerate but always diminish its swiftness:  for then ye pressure shall be more than half diminished and ye acceleration necessarily cease much, and it will go always diminishing to ye end.  It is experimented in a pipe of glass of 5 feet heigh, of 10 lines large, and of two lines ye hole, divided into 5 parts, that ye first will pass in 7 measures of time, ye second and 3 in 6, and ye 4th in 7 near, and ye rest always diminishing:  Whence it follows that in such a pipe there is 2 different places, one towards ye top and ye other towards ye middle of ye pipe where ye water descends with ye same swiftness:  Hence is seen that it is impossible for ye water to descend uniformly along cylindric vessels what ever are their largenesses their heights and ye holes or ajutages [[space]] for if ye weight wch it hat in H I joyned to ye impulse of its swiftness makes it go out with a certain swiftness thrô K ye impulse of ye same swiftness;  if it preserves it, joyned to ye weight it hath in L M, wch will be less will make it go out less swift and by consequence the upper water will descend less swift in L M than in H I, whence it follows than if at ye beginning ye upper water diminisheth its swiftness it will diminish to ye end.

Transcription Notes:
mandc: Reviewed, Amended image description. I'm not sure if Mariott didn't use "J" in his diagrams, or whether his translators read his "J"-looking I's as J's. Even in the Desaguliers translation diagrams there are only "I's" no "J's." http://echo.mpiwg-berlin.mpg.de/ECHOdocuView?url=%2Fpermanent%2Flibrary%2FQERNH1MN%2Fpageimg&mode=imagepath&pn=254&ww=0.0649&wh=0.2074&wx=0.6652&wy=0.0756 "Ajutages" French for "nozzle."