110 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



[A PRIL, 



7 —Cranes being washed down on the breakwater. 

 e'.-TMe ebbing, barometer risioi!, and sea breaking In flye fathoms. 

 9.— Small waves ha»e ran into large ones. 

 10.— High water. 

 11. — Swell iubsiding. 



12.-These waves raised by the south-west wind of yesterday. ,.„.,.,,,,, 



13 and 14. -These waves indicate an approaching south-west wind as they subside. 

 These results were noted with the greatest care, and niaj be taken as 

 pretty correct. AVithoul goiDg into a discussion of the very many results 

 that may be obtained by analyzing the table, I may state two or three 



f>4pt4 VIZ ' ^^ 



Ist'.-The velocity of waves is retarded as they advance into shoaler 

 water. I have actually seen a wave overtaken and emerge into another, 



2nd".— The velocity of waves is not dependent on their height, No. 8 and 



3,.d iThese experiments on a large scale appear to prove a result ob- 

 tained by Mr. Scott Russell on a small scale, viz., that when the depth of 

 tl.e water equals the height of a wave, it breaks, and becomes a wave of 

 translation. (See No. 8, remarks.) 



4th -Deep water facilitates the undulations of waves, (September 28th, 

 No. 6 and 7), the tide rose eight feet, and the increase in velocity of Uie 

 waves was one-and-a-half feet per second. 



Leaving your readers to make comparisons or draw conclusions, I may 

 briefly assert that the hydrostatic and hydrodynamic force that water ex- 

 erts is far from being so well understood as it should be by those who as- 

 sume the duties or appellation of "civil engineer." The man who con- 

 trived the huge iron tank, which burst the other day at Liverpool, when 

 only two-thirds full, destroying much property, and drowning several per- 

 sons, knew nothing of the pressure that his tank would have to sustain 

 when filled with water. The hydrostatic pressure at any depth, is as the 

 anuare of the depth = the sum of all the pressures above it.» In comput- 

 ing the force that a wave is capable of exerting upon a solid immersed in 

 the sea we have to take into consideration the rate at which the water 

 moves or impinges against the solid, in addition to the hydrostatic pressure 

 "poa it. There are many gentlemen who add C.E. to their names, and 

 who believe that the impulse of a volume of water iu motion upon a solid 

 gtructure opposing it, will be as the volume into the velocity, as is the 

 case when one solid impinges upon another, as a mass of ice upon a stone 

 But a little reflection will convince us that the force which a volume of 

 water moving exerts upon a solid obstacle, is not proportional to the velo- 

 Ty of water but to the s,uare of its velocity. The velocity with w ich a 

 wave is thrown forward is equal to the velocity with which the unduluUon 

 was previously moving, and although a very high wave is always danger- 

 o«s, it is not always the very highest waves that are the most destructive 



If reference be made to the table of observations, it will be seen that 

 No. 7 had waves moving at the rate of forty-six feet per second ; these 

 waves were far apart, and of middling height. They were however 

 washing the huge blocks of marble about on the breakwater, and knocking 

 down the cranes upon it, whilst much higher and more crowded waves 

 moving at the rate of 41-8 feet per second, were less destructive to the 



" The ett'^btin'g, (ceteris parib„s).as the square of the 'e'ocity, we may 

 estimate what the height of the waves, moving at the rale o 46 fee,, shou d 

 Te, to equal the impulse of the waves 27 feet high, and travelling at the 

 rate of 41-8 feet per second. 



Put X - the required height. . , , r oo c.„, 



Then 41-82x27 =46^ x. Now by this equation the value of .r = 22 feet. 

 Hence it would appear the height of the waves on the 28th of September 

 must have been greater than twenty-two feet to produce the lesults upon 

 the breakwater, although their height was certainly less than the height 

 of those measured on the following day. ^^_^^^^^ ^^^^^^^^^ 



— •~ T r," V. „.w.^,;,„ hrrr It is the total amount of pleasure on the vertical 



,id^s^f"L'l.nk '.^hiVr;arfe's'a?thl sqiLr: of the depth-the pressure on any one po,„t 

 varies as the depth simply. resistnnre of the wave does not follow 



We are told further on, in he '« • '^^t;^ ^','',\^;',fr.he velocity. Views so vague as 

 the laws of impact of so'.ds. bu '^"'"■' »J '^'^h' "^s upon him to condemn the philoso. 

 these ounht not lo be e.prcssea ' V » ""J^" "",''( t^e resistance of fluids varies as the 

 ph, of others. 1 1 is indee.l "»''"''V »'*""'?i ''V, „ „inUy But this law is only approxi- 

 extent of surface and Oie square oahe velocity 00^^^^^^^ „, ,n,th. as that can only be 



S^risTnti'M-rcltre'rim:-: «n'd'cannoTbr;r"ved by indepeudent reason,ng.-[Ed. 

 C. E,& A. Journal.] 



ON THE TEMPERATURE OF THE EARTH AND SEA. 



A Lecture on this subject was delivered at the Royal Institution, by Mr. 

 S. A. Tayliir. He observed, that the atmosphere is an ;erial film sur- 

 rounding the earth, but, although of almost inappreciable thinness when 

 compared with the earth's diameter, it forms a non-conducting investment 

 resisting the radiation of terrestrial heat into space. The mean density of 

 the earth, according to Haily, is 5 CO, or about twice 28, the density of 

 rocks and strata constituting its surface. We infer from hence that the 

 mass of the earth, must be formed of materials lighter than the common 

 metals, as iron, tin, lead, &c. Its specific gravity falls between that of 

 titanium and tellurium. From careful inquiry it appears that the tempe- 

 rature of the surface of this planet depends entirely on heat acquired from 

 the sun. Part of the heat thus received is conducted to a certain depth 

 below the earth's surface ; and part radiates into space. The greatest 

 natural cold on the surface was observed by Erraan at Yakutsk, the capital 

 of Eastern Siberia, where the thermometer stood at 72 deg. below the zero 

 of Fahrenheit. The temperature of space beyond the limits of the atmo- 

 sphere must therefore be much colder — too cold to admit of the mainten- 

 ance of life under its present conditions. The heat of the sun penetrates 

 the earlh to but a very small depth. Diurnal variations of temperature are 

 not perceived below two or three feet, while the annual variations do not 

 affect the earth's crust below l-400,000lh of the diameter of this planet. 

 On the alternate heating and cooling of this film of depth depend the vicis- 

 situdes of climates, seasons, aud cycles of years. 



Mr. Taylor then stated, that, at a certain depth below the earth's sur- 

 face iliere is a stratum at which the thermometer is almost stationary. 

 This stratum is consequeully termed the stratum of inrariahic temperature. 

 The depih of this stratum depends— 1st, on the directness wilh which the 

 sun's rays fall ; and, 2nd, on the conducting power of the superficial strata. 

 It must, therefore, be dilTerent at different localities. At Paris the depth 

 of this stratum has been accurately ascertained to be 90 feet below the sur- 

 face, at which deplh the temperature has, for 50 years, remained constant 

 at 53 deg. Fah. In other different parts of the world, this stratum varies 

 in depth from reasons already assigned. In the tropics it is three or four 

 feet, iu the temperate regions from 55 to CO feet below the surface, while 

 in the regions of extreme cold, solar influence does not extend beyond three 

 or four feet, the ground below this deplh being found always frozen, to the 

 extent of 400 feet. Generally, however, the temperature of this invariable 

 stratum differs but little from the mean temperature of the place. Mr. 

 Taylor then directed attention to the important aud universal truth, that, 

 when carried below this stratum of invariable temperature, the thermome- 

 ter rises. The rise is not, however, the same at all depths in all places 

 As there are isothermal lines on the earth's surface, so there are iso-geo- 

 thermal lines beneath it. Many localities, as five of the principal mines in 

 Cornwall, the well of(JreneUe at Paris, the Monkwearinoutli mine of 

 Sunderland, Joseph's Well at Cairo, &c., were noticed as indicating the 

 great curvature of the iso-geothermal line. 

 The theory of the existence of internal heat was then established from — 



1. This progressive rise of the thermometer in descending inlo mines and 

 other excavations. 



2. The high temperature of the water of artesian wells. 



3. The high temperature of natural thermal baths or springs. 



4. The phenomena of volcanic eruptions aud earthquakes. 



From accurate examination of these sources of inquiry, there has been 

 found that the thermometer rises in mines one degree for about every 50 

 feet of depth ; a result confirmed by the fact that the temperature of water 

 in artesian wells increases in about the same proportion to their depth. 

 The heat of thermal springs has been found equal to that of boiling water, 

 and the perfectly fused condition of substances ejected from volcanoes in- 

 dicates a tempeiatiiie of 1000 deg. The opinions of various philosophers 

 respecting the cause of the central heat of the world viere reviewed. Buffon 

 held that the earth was a vitrified ball in the act of cooling ; Leslie and 

 Halley that it was a hollow sphere, made up of stories like a house ; 

 others that the interior of the earth is iu a perfectly molten state, the heat 

 at twenty miles below the surface being suflicient to melt granile. Having 

 pointed out llie objections to these various hypotheses, Mr. Taj lor aflinned, 

 as an apparently certain fact, that this internal heat does not ali'ect the 

 temperature of the earth's surface. He particularly dwelt on a calculation 

 made by Arag", that if iu the period of 2000 years the earth had cooled 

 only l-300lh of a degree, the fact would have been indicated by adiftereaca 

 in the length of the day, in consequence of that contraction of its diameter 



