JDP 



JUR 



the centre of the primary, slower the 

 more distant they are, and at the greatest 

 distance of all they appear for a short time 

 to be stationary. 



From this account of the system of Ju- 

 piter and his satellites, it is evident that 

 occultations of them must frequently hap- 

 pen by their going 1 behind their primary, 

 or by coming in betwixt us and it. The 

 former takes place when they proceed to- 

 wards the middle of their upper semi- 

 circle ; the latter, when they pass through 

 the same part of their inferior semi-circle. 

 Occultations of the former kind hap- 

 pen to the first and second satellites ; at 

 every revolution, the third very rarely 

 escapes an occultation ; but the fourth 

 more frequently, by reason of its greater 

 distance. 



It is seldom that a satellite can be dis- 

 covered upon the disk of Jupiter, even by 

 the best telescopes, excepting at its 

 first entrance, when, by reason of its be- 

 ing more directly illuminated by the rays 

 of the sun than the planet itself, it appears 

 like a lucid spot upon it. Sometimes, 

 however, a satellite in passing over the 

 disk appears like a dark spot, and is easi- 

 ly to be distinguished. This is supposed to 

 be owing to spots on the body of these se- 

 condary planets ; and it is remarkable, that 

 the same satellite has been known to pass 

 over the disk at one time as a dark spot, 

 and at another so luminous that it could 

 not be distinguished from Jupiter himself, 

 except at its coming on and going oft'. 

 When the satellites pass through their in- 

 ferior semi-circles, they may cast a sha- 

 dow upon their primary, and thus cause an 

 eclipse of the sun to his inhabitants, if 

 there are any ; and in some situations this 

 shadow may be observed going before or 

 following the satellite. On the other hand, 

 in passing through their superior semi- 

 circles, the satellites may be eclipsed in 

 the same manner as our moon, by pass- 

 ing through the shadow of Jupiter; and 

 this is actually the case with the first, se- 

 cond, and third of these bodies : but the 

 fourth, by reason of the largeness of 

 its orbit, passes sometimes above or be- 

 low the shadow, as is the case with our 

 moon. 



The beginnings and endings of these 

 eclipses are easily seen by a telescope, 

 when the earth is in a proper situation 

 with regard to Jupiter and the sun ; but 

 when this or any other planet is in con- 

 junction with the sun, the superior bright- 

 ness of that luminary renders both it and 

 the satellites invisible. From the time of 

 its first appearing after a conjunction, 



until near the opposition, only the immer^ 

 sions of the satellites into his shadow, or 

 the beginnings of the eclipses, are visible ; 

 at the opposition, only the occultations of 

 the satellites, by going behind or coming 

 before their primary, are observable : 

 and from the opposition to the conjunc- 

 tion, only the immersions, or end of the 

 eclipses, are to be seen. This is ex- 

 actly true in the first satellite, of which 

 we can never see an immersion with its 

 immediately subsequent emersion : and 

 it is but rarely that they can be both 

 seen in the second ; as, in order to their 

 being so, that satellite must be near one 

 of its limits, at the same time that the 

 planet is near his perihelion and qua- 

 drature with the, sun. With regard to 

 the third, when Jupiter is more than 

 forty -six degrees from conjunction with, 

 or opposition to the sun, both its im- 

 mersions and immediately subsequent 

 emersions are visible; as they likewise 

 are in the fourth, when the distance of 

 Jupiter from conjunction or opposition is 

 twenty-four degrees. 



JURATS, magistrates in the nature 

 of Aldermen, for the government of 

 several corporations. Thus we meet with 

 the Mayor and Jurats of Maidstone, Rye, 

 &c. 



JURY, a certain number of persons 

 sworn to inquire of and try some mat- 

 ter of fact, and to declare the truth upon 

 such evidence as shall be laid before 

 them. The jury are sworn judges up- 

 on all evidence in any matter of fact. 

 Juries may be divided into two kinds, 

 common and speciaf. A common jury 

 is such as is returned by the sheriff; 

 according to the directions of the statute 

 3 George II. cap. 25, which appoints 

 that the sheriff's officer shall not return 

 a separate pannel for every separate 

 cause, but one and the same pannel for 

 every cause to be tried at the same as- 

 sizes, containing not less than forty-eight, 

 nor more than seventy-two jurors ; and 

 their names being written on tickets shall 

 be put into a box or glass, and when each 

 cause is called, twelve of those persons, 

 whose names shall be first drawn out of 

 the box, shall be sworn upon a jury, un- 

 less absent, challenged, or excused. 

 When a sufficient number of persons 

 are impannelled, they are then separate- 

 ly sworn well and truly to try the issue 

 between the parties, and a true verdict 

 give according to the evidence. 



Special juries were originally introduc- 

 ed in trials at bar, when the causes were 

 of too great nicety for the discussion of 



