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thing every now and then to post into a Mental Ledger , where the real amount of Information and Balance of Intellectual Profit might be fairly and simply exhibited . This Mr . Murray has done , as to North sfmerica , and very much to our satisfaction . His work contains the
essence of between two and three hundred volumes { probably more ) of all sizes , in several languages , and of all ages , from the Saga of King Orlaf Tryggeson to the Travels of Captain Basil Hall . The facts are selected , arranged , and accompanied by their authorities ; and the result is a clear and impartial view of the United States . To this is added an Account of
Canada ; and a very interesting abridgment of the narratives of the several expeditions ( as well as those of individual adventurers ) for the discovery of a Northwest Passage . The work is a valuable addition to Mr . Murray ' s former publications , of a similar description , on Asia and Africa .
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Critical Notices . —Miscellaneous . 61
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binding ring is thus heated and expanded sooner than the stopper , and so becomes slack or loose upon it . f < Pipes for conveying hot water , steam , hot air , &c , if of considerable length , must have joinings that allow a degree of shortening and lengthening , otherwise a change of temperature may
destroy them . An incompetent person undertook to warm a large manufactory by steam from one boiler . He laid a rigid rnaiti pipe along a passage , and opened lateral branches through holes into the several apartments , but on his first admitting the steam , the expausioti of the main pipe tore it away from all its branches .
" In an iron railing , a gate which , during a cold day , may be loose and easily shut or opened , in a warm day may stick , owing to there being greater expansion of it and of the neighbouring railing , than of the earth on which they are placed . Thus also the centre of the arch of an iron bridge is higher in warm than in cold weather ; while , on the contrary , in a suspension or chain bridge , the centre is lowered .
" The iron pillars now so much used to support the front walls of houses , of which the ground stories serve as shops with spacious windows , iu warm weather really lift up the wall which rests upon them , and in cold weather allow it again to sink or subside—in a degree considerably greater than if the wall were brick from top to bottom .
" In some situations , ( as lately was seen in the beautiful steeple of Bow Church , in London , ) where the stones of a building are held together by clamps or bars of iron with their ends bent into them , the expansion in summer of these clamps will force the stones apart
sufficiently for dust ot sandy particles to lodge between them ; aud then , on the return of winter , the stones not being at liberty to close as before , will cause the ends of the shortened clamp . s to be drawn out , aud the effect increasing with each revolving year , the structure will at last be loosened and may fall .
* ' The pitch of a piano-forte or harp is lowered in a warm day or in a warm room , owing to the expansion of the strings being greater than of the wooden frame-work ; and in cold the reverse will happen . A harp or piano , which is well tuned in a morning drawing-room , cannot be perfectly in tune when the crowded evening party hat * heated the
room . " Bell-wires too alack in summer , may be of the proper length iu winter . "—Pp . 66 , 67 .
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Art . XII . — Elements of Physics , or Natural Philosophy , General and Medical , explained independently of Technical Mathematics . 2 Vola . Vol . II . Part I ., comprehending " the Subjects of Heat and Light . By Neil Arnott , M D ., of the Royal College of Physicians . 8 vo . Longman and Co . London . 1829 .
A very useful task was that undertaken by Dr . Arnott in the commencement of this work , and very ably is he continuing and extending it . There are few who can devote themselves to scientific investigations , but all have occasion for some acquaintance with the results of those
investigations . In many cases , too , the proof is independent of the mathematical technicalities by which it has been encumbered , aud may be presented , together with the result , in a luc" and popular form . All that is really and practically valuable in science may thus be brought within common reach . Of the
interestnig and useful way in which this is done in the work before us , the following specimen may be taken , which relates to the effect of heat in expanding different bodies : " A cannon-ball , when heated , cannot be made to enter au opening , through which , when cold , it passes readily .
* ' A glass stopper sticking fast in the neck of a bottle often may be released by surrounding the neck with a cloth taken out of warm water—or by immersing the bottle in the water up to the neck : the
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Citation
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Monthly Repository (1806-1838) and Unitarian Chronicle (1832-1833), Jan. 2, 1830, page 61, in the Nineteenth-Century Serials Edition (2008; 2018) ncse.ac.uk/periodicals/mruc/issues/vm2-ncseproduct2580/page/61/
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