GREAT BOOKa 



77 



Fahrenlu-it't Scale, which is best known in England, divides the 

 spaco between tho two fixed points the freezing and boiling 

 of water into 180. Fahrenheit fixed as his zero (0) 

 iiporaturo which had been observed at Dantzio in I ,"'.', 

 and which ho found could always bo reproduced by mixing salt 

 and xnow together. Ho therefore, though erroneously, con- 

 cluded Hint this was nature's zero tho absolute zero. Ho com- 

 puted that his instrument contained at 0, 11,124 parU of 

 y, and at the freezing point 11,156 parts; henco ho 

 divided the space botweou zero and the freezing point of water 

 J IKirts (11,156 11,124 = 32). From this point to 

 hoiling point contained 180 of these degrees, therefore 212 

 indicates the boiling point of water. 



It was Fahrenheit who first used mercury for purposes of 

 thennometry. 



The Centigrade Scale was introduced by the Swedish philo- 

 sopher, Celsius, who was a professor at Upsal. In it the freezing 

 point is tho zero, and the boiling 

 point 100. This scale is tho one 

 generally in use in the scientific world. 

 Reaumur's Scale was proposed by 

 a French philosopher of that name 

 in 1731. His thermometers were 

 constructed with alcohol of such a 

 strength, that 1,000 parts at the 

 freezing point of water became 1,080 

 at its boiling point. Hence tho in- 

 terval between tho two fixed points 

 was divided into 80. 



It is evident that these scales are 

 quite arbitrary, and that we have 

 only two fixed points. It is neces- 

 sary, therefore, to determine these 

 before the instrument can be gra- 

 duated. 



TO FIND THE FREEZING POINT OF 

 WATER. 



Fig. 3. Water does not always freeze at 



the samo temperature. If water be 



gradually reduced in temperature, and bo kept perfectly still, 3 

 or 4 degrees below Cent, may be reached before tho ice will 

 begin to form ; but ice invariably melts at a fixed temperature. 

 Therefore immerse the thermometer in melting ice, and mark the 

 point to which the mercury falls. 



TO FIX THE BOILING POINT. 



Place the thermometer in a vessel such as is represented in 

 Fig. 3, in which water is boiling, and the steam generated 

 passes round the walls, c c, of the p p. jj_ 



partition to make its escape at B. 

 Thus the compartment D in which the 

 instrument is placed, being enclosed ^f 



by steam, cannot be affected by the 



temperature of the air. 



A is a bent tube of glass, open at 

 each end, in which is a little mercury. 

 So long as the exit of tho steam from 

 B is not impeded, the steam will be of 

 a uniform temperature. If the steam 

 could not escape at B, it would be in- 

 dicated by A, for if the pressure of the 

 steam increase, the mercury will not 

 remain level. The point at which the 

 mercury in the thermometer stands, is 

 marked as the " boiling point." 



The tube is then mounted on a piece 

 of board, upon which is marked the 

 scale. If Fahrenheit's (Fig. 4 a), the 



Fig. 4. 



space between the two fixed points is divided into 180 equal 

 parts, which are produced above and below 32 and 212 (which 

 indicate the freezing and boiling points), as far as is required. 

 For Centigrade (Fig. 4 b), the division is into 100, the freezing 

 point being ; for Reaumur (Fig. 4 c), into 80. Fig. 4 com- 

 pares at a glance these scales. 



TO CONVERT DEGREES OF ONE SCALE INTO ANOTHER. 

 Since 180 Falir. = 100 Ceut. = 80 Beau. 

 Therefore 1 Four. = 4 Cent. = j Beau. 



The reason of the following rule* will be at onoe evident ; 



To transfer Fahrenheit degree* to the other wale*, snbtraet 



32 P , in order that the number of degree* from the fmiiiij 



point may bo ascertained. These multiplied by | will give the 



equivalent number of Centigrade, and by | the required Rnenmnr 



lll'^rrcs. 



To reduce Centigrade and Reaumur degree* to the Fahrenheit 

 scale, multiply by | and f respectively, and add 32. 



If tho temperature be below the zero in any of the itnlea. 



inimiH ( ) ia placed before the number, thus : 5 Fahren- 

 heit means 37 below freezing. 



In verifying the following, the student will become expert hi 

 these conversions : 



Fahr. 



185 = 



158 = 



126 = 



5 = 



- 13 = 



Cent. 

 85 

 70 

 52-2 

 -15 

 -25 

 38-4 



417 



12 



20" 



31-5 



In a good thermometer, the mercury ought to run to the end 

 of the tube with a "click" when it is inverted, proving the 

 absence of air, and completely fill the tube ; and when placed 

 in melting ice, the mercury ought to stand at 0. It frequently 

 happens that the mercury stands above tho freezing point. This 

 error is called " the displacement of zero," and is caused by the 

 curious fact that sometimes the bulb does not perfectly contract 

 for two or three years after it was blown ; so that for the beet 

 instruments the bulbs are kept for more than that time unfilled. 



If the bulb be made of thick glass, it is less likely to change. 



It is plain that in a thermometer we are not given the 

 absolute expansion of the mercury, but the difference between 

 the expansion of the mercury and that of the glass. Mercury 

 expands about seven times more than glass. 



GREAT BOOKS. 



V. SHAKESPEARE'S PLATS. 



OF all " great books " known to the English-speaking race, 

 the plays of Shakespeare are those which most immediately and 

 most powerfully occur to the mind. They are the most varied 

 and the most extraordinary productions of the English genius ; 

 familiar to us in the library and on the stage ; still more fami- 

 liar in those countless allusions, phrases, and well-known figures, 

 which have become part of our common life ; illustrated in a 

 thousand ways by pictorial art ; and so identified with the whole 

 structure of our minds that it is difficult even for the nnin- 

 structed to help thinking Shakespeare when they suppose them 

 selves to be only using the words of ordinary parlance. It 

 cannot, indeed, be said of this wonderful man that he helped to 

 form the English language, for it was formed when he began to 

 write, but he undoubtedly helped to fix it. The dramas of 

 Shakespeare, and the authorised translation of the Bible, are 

 the noblest standards of English that we possess. Setting 

 merely scientific and technical language aside, it is impossible 

 to conceive any range of thought which the tongue of Shake- 

 speare is not able to make articulate and eloquent. We hare 

 never advanced beyond that vivid and vital speech. 



Great as are the plays of our chief poet, they will appear tUl 

 greater if wo consider the state of dramatic literature in this 

 corntry at tho time when their author began his career. To 

 the " miracle-plays " of the middle ages which were mere 

 shows, and cannot be considered as literature had succeeded 

 a number of " moralities," comedies, interludes, and other en- 

 tertainments of a very rudo and primitive description. It was 

 not until the reign of Queen Elizabeth that anything worthy to 

 bo called the poetic drama was composed in England; and 

 although some writers preceded Shakespeare by a few years, 

 tragedy and comedy, as we now understand them, did not 

 attain their full development until about the period when the 

 grand master himself arose in the splendour of his youthful 

 genius. It is generally thought (for we have no certain records 

 on the subject) that Shakespeare's earliest play appeared about 

 1590. As the poet was born in 1564, and was therefore six- 

 and-twenty in the later year, it is probable that he had been 

 engaged in dramatic composition some time before any one 

 of his plays obtained a public hearing. Twenty years earlier 



