LESSON'S IN' ASTUONOMV. 



PROMPT. The term of credit or period filed upon by con- 

 tract for payment of the purohane money for produce. 



PROOF IN UANKKUPTCY. The requisite proof, by affidavit 

 or oath, of the correctness of any claim made upon a bank- 

 rupt's eiitate. 



PRO UATA. A Latin term signifying proportionally. 



PROTEST or A BILL. A declaration made by a notary or 

 T.M< in of the proHentation of a bill (either for acceptance 

 or for payment), of the reply received, and of the refusal to 

 accept or pay. 



i'ltoTK.sr (Snip's). A declaration, made by the master and 

 crew upon oath, of the particular circumstances under which 

 any injury to a ship or cauae of damage to her cargo has arisen. 



PROXY. Authority placed in the hands of a deputy, as a 

 substitute for its personal exercise. 



QUARANTINE. A regulation in force at certain ports, cutting 

 off and interdicting for definite periods all communication 

 between ships and the shore, on their arrival from places com- 

 monly affected with contagions diseases. 



QUID PRO Quo. A Latin phrase, signifying one thing for 

 another. The mutual consideration in contracts. 



QUOTATIONS. Stated prices. It is usual to quote the prices of 

 certain articles, inclusive of the charges incurred in their delivery 

 on board ship, which are termed quotation* f. o. b, (free on board). 



RATR OK EXCHANQE. The actual price at which bills on a 

 foreign country can be bought. 



REAL, PROPERTY. Property that cannot be moved, such as 

 land, houses, etc. 



REBATE. A return of discount by bankers and others upon 

 bills taken up by the discounter previous to their arriving at 

 maturity. 



LESSONS IN ASTRONOMY. XIX. 



TEMPORARY STARS CLUSTERS AND NEBULA THE NEBULAR 



HYPOTHESIS CONCLUSION. 



CLOSELY allied to the variable stars are the now or temporary 

 stars, which have at times attracted so much attention. Several 

 such appearances have been recorded ; one of the most remark- 

 able, however, is that observed by Tycho Brahe, in November, 

 1572. This star seems to have burst forth very suddenly, as it 

 is said that the constellation Cassiopeia, in which it appeared, 

 had been carefully observed by an astronomer only two evenings 

 before the star was seen, and that then no trace of it was 

 observed. The star continued visible for about sixteen months, 

 gradually becoming fainter till it disappeared. Its brilliancy at 

 first was so great that it cast a sensible shadow, and it is said 

 to have been visible by day. In 945 and 1204 stars had ap- 

 peared in the same constellation in a somewhat similar manner, 

 and as the intervals between the three dates are almost 

 equal, it has been conjectured that they might bo three appear- 

 ances of the same object. If this be the case, we may in the 

 course of a few years gaze again upon this star, which in former 

 times attracted so much attention. 



Another temporary star of considerable brilliancy appeared 

 in the year 1004, and was also carefully observed by Brahe. 

 Modern times have, however, furnished us with several instances 

 of this kind. In 1848 Mr. Hind observed a new star in 

 Ophiuchus. It increased in brilliancy to the fourth magnitude, 

 but subsequently decreased to the eleventh or twelfth, at which 

 it now remains. 



In 1806 a new star also appeared in the Northern Crown, and 

 was very minutely examined. It had been previously noted as 

 of the ninth magnitude, but in May it suddenly shone out as a 

 second magnitude star ; its light, however, diminished very 

 rapidly indeed for some time. Attention was immediately 

 directed to it, the spectroscope being now available for its 

 observation. This instrument showed, in addition to the ordi- 

 nary spectrum of the star, a second spectrum of bright lines, 

 prominent among which were those indicative of burning hydro- 

 gen, so that it appears that, in this instance, a sudden blaze 

 was produced by incandescent hydrogen and other substances. 



If wo compare old star catalogues with those of the present 

 day, wo find, in addition to many changes of magnitude, that 

 several stars whoso places are there recorded are now no longer 

 to be found ; and, on the other hand, we find that some of those 

 now known are not recorded in the old lists, although their 

 brilliancy ie considerable, and would probably have ensured their 



insertion ha/1 they been vuiblo. Doubtless, in many of 

 cases, the discrepancy may urine from error* of observation ; bat 

 there a no doubt that many stars have altogether disappeared, 



ami it is not improbable that some of these may be variable*, 

 which after a more or less prolonged absence may again become 

 visible. 



us explanations have been offered to account for these 

 phenomena. Some imagine the star to rotate, and one por- 

 tion of ita Rurfaoe to bo more luminous than another ; other* 

 suppose that a planet may revolve around the star, and thna 

 eclipse its light. Nono of the theories stated, however, appear 

 satisfactory, and we can only wait in the hope that future 

 research, aided by the spectroscope and by more refined instru- 

 ments, may throw froHU light on the whole subject. All the; 

 variables arc being closely watched with this object. 



< -3 the stars and planets, we easily distinguish in the sky 

 various groups called clusters or nebulae. These are usually 

 divided into 



Irregular Groups, more or less visible to the naked eye ; 



solved by a good telescope ; and 



Nob nice, many of which are irresolvable with the most 

 powerful telescopes yet made. 



There aro many examples of the first class, among which may 

 bo mentioned Pracsepe, or the Beehive, and the Sword Handle 

 in Perseus, both of which are very beautiful objects for the 

 telescope. Very many objects of the second class have also 

 been noted. lu ordinary telescopes they appear for the most 

 part as faint cloudy masses ; but as more powerful instruments 

 arc directed to them they begin to resolve into stars placed very 

 close together. Every increase yet made in the power of the 

 telescope has had the effect of resolving more of these clusters. 



In shape and appearance they vary greatly, some being globu- 

 lar or elliptical masses, while others present very strange forms. 

 The Great Nebula in Orion (Fig. 46), and the Dumb Bell Nebula 

 in Vulpecula (see " Recreative Science," XIV., Vol. V., p. 313, 

 for illustration of this nebula), are examples of this. Many, 

 however, can only be partially resolved, films of misty matter, 

 I gradually fading away, being distinguishable apart from the 

 stars. No defined lino can indeed be drawn to divide between 

 clusters and nebulae. 



So great is the number of these objects that a catalogue of 

 them, compiled by Sir John Herschel, contains no less than 5,079. 



Of their distances we can form no conception. If we attempt- 

 to determine it by the space-penetrating power of the telescoj>es 

 required to resolve them, we find it to be such that light would 

 take many thousand years to travel from them to us. 



Some idea of the extreme faintness of these objects may be 

 formed from the estimate which has been made that their light 

 varies from l a to 5^ of that of a sperm canal 3 a quarter of a. 

 mile distant. 



Some of these nebulae have a spiral form. The best known 

 of these is in the constellation Canes Venatici. In Sir John 

 Herschel's telescope it presented the appearance shown at 

 Fig. 47, a bright globular cluster, partially resolvable, occupying 

 the centre, while surrounding it is a ring divided for nearly half 

 tho circumference into two bands. Just outside this is a second 

 cluster. When, however, Lord Rosse's magnificent reflector 

 was turned to this nebula, it presented quite a different 

 appearance (Fig. 48), and seemed to consist of spiral coils of 

 nebulous matter, with which tho outer portion was connected. 

 Several other spiral nobulao are known. 



Besides those masses, nebulous stars may bo observed in dif- 

 ferent parts of the sky. These are usually of a circular form, 

 and consist of a star surrounded with a faint cloudy mass, 

 which is quite irresolvable. 



The nebulae are not distributed by any means uniformly over 

 tho surface of the sky, the majority being situated in a zone 

 crossing the Milky Way at right angles. In the constellation 

 Virgo there is the greatest aggregation of them, one portion of 

 it being known as tho nebulous region of Virgo ; and in the 

 southern hemisphere, not far removed from the pole, are two 

 brilliant cloud-like patches called the Magellanio Clouds or 

 Nubeculos. These, when examined by the telescope, are found to 

 consist of large numbers of stars, clusters, and nebulas collected 

 together. In appearance they somewhat resemble a portion of 

 the Milky Way, but they ore quite distinct from it. 



Some of the nebulae, like some of the stars already referred 

 to, are found to be variable. In October, 1852, Mr. Hind dia- 



