T E R 



840 



I K R 



advantageous in lea ' his station* 



or t,, .instruction of In- instruments, so wto ]mt 



r-.iMi- circumstances lor deter- 

 mining the la from observation. 



In v -is M. Arago, ut the Observatory of Paris, 



niHilc M ' tin- irregular changes to 



which tin- declination of tin- needle is subject : mul M. 

 Kuptter having about tht- same time made similar ob- 

 ervir Ls *n, * comparison of the results led to the 



that the perturbations wcic -imultancou- at 

 those places, though tlu-y (littered in longitude al>ov. 



aaikable circumstance immeiliately attract- 

 ed the notice of philosophers, anil a plan for making 

 simultaneous observations in many different places was 

 organized 1 1\ M. de llumboldt in IN'J7. Kor this purpose 

 magnetic .stations were established at Herlin and r rey- 

 berg: and the Imperial Academy of Russia, entering wiih 

 zeal into the p; -< <l a chain of stations to ! 



tended from St. Petersburg to Pekin, at all which jilaees 

 simultaneous observations were appointed to he made 

 se\en times in the year, at intervals of one hour, during 

 twenty-four hours. 



In 1834 Professor Gauss discovered the fact that the 

 synchronism of the perturbations was not confined to the 

 decimation of the needle, but that every deviation at one 

 place of observation had its counterpart at another ; and 

 ne was therefore induced to recommend a plan of simul- 

 taneous observations at intervals of five minutes during 

 twenty-four hours, four times in the year. This sug- 

 gestion was immediately adopted, and on the Continent 

 magnetic stations were formed at more than twenty cities 

 of Europe, from Dublin to St. Petersburg. The 'British 

 Government and the East India Company also, besides tin- 

 principal observatories of the former at Greenwich and 

 Dublin, immediately sanctioned the formation of magnetic 

 stations, under the direction of scientific officers, at St. 

 Helena and the Cape of Good Hope, in Canada, the East 

 Indies and New South Wales : and in the present 

 ditionto the antarctic regions under < 'aptain .1. C. Ross, one 

 of the leading objects is the determination of the magnetic 

 elements in that remote part of the world. The system of 

 simultaneous observations at numerous and stated times of 

 the year, which has been organized in Europe, is to be con- 

 formed tp by all the British observers: and the Royal 

 :y of London has caused an able Report of the ob- 

 .ntifie inquiry in physics to be drawn up for 

 the use of travellers in" general", and particularly for the 

 persons who have been appointed to take part in the ob- 

 servations respecting magnetism and meteorology. 



The instruments employed for determining the elements 

 of terrestrial magnetism. 'and the variations to which they 

 are subject, are of three kinds; the declination magneto- 

 meter; and the horizontal and vertical force magnet o- 

 :s. The first is a needle or bar, from twelve to 

 fifteen inches in length, nearly one inch broad, and a 

 quarter of an inch thick, suspended in a horizontal position 

 in a stirrup by untwisted silk fibres about two feet long. 

 The apparatus is contained in a box, to protect it from the 

 agitation of the air, with two apertures in opposite j n-i- 

 tions; one of these is for illuminating the scale, ami the 

 other is used for the readings, which are taken by mean- of 

 a telescope at a distance. For a description of such an 

 instrument and its adjustments, see Taylor's 'Scientific 

 part v. By this instrument may be observed 

 the' absolute declination, or the angle which HIP axis of the 

 needle makes with the astronomical meridian of the place, 

 the variations of the declination, and the horizontal com- 

 ponent of the earth's magnetic force. The latter is I'nund 

 nents ol d. -Mention and experiment sol' vibration : 

 and the formul I for the purpose are given 



in the work of Gauss, entitled Intensity vi- V, 



IKU . SIM- also the Report of the <"om- 

 ihe Royal S< ,11. Hut fiaus- 



initiations of intensity by the vibrations of 

 a needle are inaccurate on account of the changes which 

 nay take place in the inten-ily during the time in which 

 the vibrations continue; and i'n 1K!7 he invented anew 

 instrument, which is called a Bifilar magnetometer, for 

 the purpose of determining the horizontal intensity alone. 

 This consist* of a magnetised needle m I : hori- p 



zontally in a stirrup placed under n circular graduated 

 plate, to the tipper part of which are attached the two 

 extremities of a tine steel thread or wire. The middle, or 



the bend, of the thread pasj.es over two pulleys which are 

 lived 111 the upp' the building; and the two parts 



of the thrta.l h:i parallel to one 



another, when the needle rests in the magnetic meridian. 

 Then, on turning the whole apparati. 



to make the needle deviate Irom the magnetic meridian, 

 the tendency ol the needle to return to it> Inrnu-r pu-ition 

 causes the threads to assume directions i,blii|ue to each 

 other: and there is some position of the needle in which 

 Its dircctiv c loree is equal to the force by which the tl; 

 resist being made to cross each others directions: it is 

 to adjust the instrument so that, when this equi- 

 librium takes place, the needle shall lie in a direction at 

 right angles to the plane of the magnetic meridian. The 

 torsion of the threads by which the needle is made : 

 suuie that position indicates the horizontal component of 

 the magnetic force, and every change in the intensity of 

 the latter affects in a direct manner the position of the 

 needle. The magnetized bar in use at the (iottmgcn ob- 

 servatory weighs i'llbs., and the length of the pair of 

 suspending threads is 17 feet. .Taylor's X< n tttil: 

 parts vi.. vii. Instruments on the same principle, but of 

 smaller dimensions, are made for ordinary occasions. 

 the Royal Society's Report. 



The vertical lone magnetometer consists of n magnetic 

 needle resting on agate planes by what are called knife- 

 edges, and it is made to assume a horizontal position by 

 means of weights : the deviations of the needle from that 

 position, when in the plane of the magnetic meridian, or in 

 a vertical plane making any angle with that meridian, 

 serve to determine the variations in the vertical component 

 of the magnetic intensity. 



Gauss observes that, on account of the simple rela- 

 tion that the horizontal and vertical components b. 

 one another, these are more proper to serve as the foun- 

 dation of a theory, than the usual expression of the mag- 

 netic force by the total intensity, the inclination, and the 

 declination; and he recommends that, in all observations, 

 the intensity in the horizontal direction should be kept 

 distinct from the other elements. 



TKRRIKR (funis /nini/iiirix T<-rr<irin*\ a variety of 



the dog remarkable ibr the eagerness and courage with 



which it goes to earth, and attacks all tho-v quadrupeds 



which come under the gamekeeper's denomination of 



in, from the Fox to the Rat. 



In the genealogical table of the different races of dogs 

 we find the Hound immediately next in descent from the 

 Shepherd dog. which is placed as the immediate descend- 

 ant of the Lapland dog, the highest in the table, and col- 

 lateral to the Hound, the '/////'<;. and liirriir. 



Lieut.-Col. Hamilton Smith (Nn/uni/ifl'n Library, Is 10 . 

 treating on the Cur Dngs, after stating that in Southern 

 Africa we have a race of small Sacalian dogs : in Arabin. 

 one of Thoan form: in India, the parent Pariah (need, ap- 

 parently captured in the woods of the country : that 

 Southern China, all Persia, Natolia, and Russia have a 

 similar predominant race of cure; and that in Europe 

 there is everywhere evidence of an originally indigenous 

 species of small dimensions, or at least ol' one. brought in 

 by the earliest colonists of the west, extending from I. up- 

 land to Spain, goes on to observe, that if we search lor 

 that kind which now seems to be the most typical, that 

 possessing innate courage, sagacity, and profitie power. 

 without training or care in breeding. these qualities are 

 found most unquestionably united in the terrier, and no- 

 where so fully marked, vvitii all the tokens of antient ori- 

 ginality, as in the rough-haired or Scottish breed. 'In 

 the terrier. Smith in continuation, ' we still see 



all the alacrity of innate confidence, all resources of spirit. 

 all the willingness to remain familiar with subteinr 

 habitations, and all the daring and combination which 

 makes him fearless in the prc-cnce of the most formidable 

 animals; for it is often noticed in India, that when the 

 bull-dog pauses, British terriers never hesitate to surround 

 and giapplc with the hy;rna. the wolf, or even the pan- 

 ther. . . . If there be an original and indigenous dog of 

 Britain, it is surely the species we have now under review : 

 for if the Irish wolf-dog, or a questionable' gaze-hound, 

 were derived from the British wolf, such a conquest over a 

 powerful and ferocious animal could scarcely have been 

 achieved without the aid and Intelligence of a previously 

 domesticated and smaller spe.-ies. But ii is more likely 

 the terrier of antiquity was of the same, race with the 



