TELESCOPE. 



vlfione frafta majora funt ; nam de facili patet per canoiios 

 fupra-dklos, quod maxima pofTuiit apparere minima, et e 

 contra, et longc dillantia vidcbuntur propinquiffime, cte con- 

 vcrfo. Nam pofl'umus iic figurare perfpicua, et taliter ca 

 ordinare refpeftu uoftri vifus ct rerum, quod frangentur ra- 

 dii, ct fledtentur quorfumcunque voluerimus, ut fub quo- 

 cunque angiilo voluerimus, videbimus rem prope vel longe. 

 Sec. Sic etiam faceremus folem et lunam et ftellas defcen- 

 dere fecundum apparentiam hie inferius, &c. :" i.e. greater 

 things than thefe may be performed by refrafted vifion ; for 

 it is eafy to underftand by the canons above-mentioned, that 

 the greatelt things may appear exceeding fmall, and on the 

 contrary : alfo that the moil remote objefts may appear juft 

 at hand, and on the contrary : for we can give fuch figures to 

 tranfparent bodies, and difpofe them in fuch order with rc- 

 fpeft to the eye and the objefts, that the rays fhall be re- 

 fra&ed and bent towards any place we pleafe ; fo that wi- 

 fhall fee the objeft near at hand or at a diftance, under any 

 angle we pleafe, &c. So that thus the fun, moon, and 

 ftars, may be made to defcend hither in appearance &c. Mr. 

 Molyneux has alfo cited another palTage out of Bacon's 

 Epillle ad Parifienfem, of the Secrets of Art and Nature, 

 cap. 5. to this purpofe : " Poffunt etiam fic figurari perfpi- 

 cua, ut longiffime pofita appareant propinqua, et e contra- 

 rio : ita quod ex incredibili diftantia legeremus literas minu- 

 tiflimas, et numeraremus res quantumque parvas, et ilellas 

 faceremus apparere quo velleraus ;" ;. e. glafles or diapha- 

 nous bodies may be formed, that the moll remote objefts 

 may appear juft at hand, and contrarily ; fo that we may 

 read the fmalltft letter at an incredible diftance, and may 

 number things though never fo fmall, and may make the 

 ftars appear as near as we pleafe. 



Dr. Smith, however, who muft be confidered as having 

 been a competent judge of this fubjeft, was unwilling to 

 allow the inference, that Bacon actually made a telefcope, 

 and conjeftures that he only conceived in liis mind how fuch 

 an inftrument might be conftruftcd ; which, by the bye, 

 is ftlll allowing the invention, though not the conftruftion, 

 to have been his. But be this as it may, we find no 

 further notice taken of any fuch inftrument as a telefcope 

 until about the year 1560, when John Baptifta Porta, a 

 Neapolitan, is faid by Wolfius to have made a telefcope ; 

 but the defcription he gave of his invention in his Magia 

 Naturalis is fo defeftive, that Kepler declared it unintel- 

 ligible ; neither does it appear that this telefcope was ufed 

 in any celeftial obfervation. Soon after this time, -viz. in 

 the year 1579, according to the account of Thomas Diggcs, 

 in his Stratifticos, his father, Leonard Digges, had learned 

 from a manufcript book of the learned Bacon, how to dif- 

 cover objefts at a diftance, by perfpeftive glafles fet at due 

 angles, when the fun fhone upon them ; but it is not evi- 

 dent whether the conftruftion refembled that of a telefcope 

 or of a camera obfcura, nor whether it was of the dioptric 

 or catoptric kind. 



According to Defcartes, .Tames Metius, while amufing 

 liimfclf with making mirrors and burning-glafles, happened 

 to look through two lenfes, one concave and the other con- 

 vex, placed by accident at a proper diftance from each other, 

 and thus difcovcred the property that fuch a combination 

 of glaftes pofleftes of (hewing objefts at a diftance ; this 

 difcovery is faid to have been neat the end of the i6th cen- 

 tury. The fame difcovery has been alio attributed to John 

 Lipperftieim, a maker of fpeftacles at Middleburgh ; but Bo- 

 rellus, in his book entitled " De vero Teleicopii Invcntore," 

 makes Janfen, or Hanfcn, (Zacliarias Joannidcs, ) another 

 maker of fpeftacles at the fame place, the real inventor of 

 the telefcope in the year 1590; and there feems to remain 

 Vol. XXXV, 



little doubt but that Janfon was entitled to the honour. 

 The account is, that after having arranged the glalTcs in a( 

 tube, tliis ingenious mcctianic haftened to prefe?it it to prince 

 Maurice, under a perfuafion that it would benefit him in his 

 wars ; but the fecret foon became public, and Lipperlhoim 

 immediately copied the invention. This firll telefcope mag- 

 nified about fifteen or fixteen times, and its inventor vifwed 

 with it tlie fpots of the moon, the body of Jupiter, and 

 even faw fome fmall ftars above and below his difc, which 

 appeared to move round him, and which therefore muft have 

 been his fatellites. From this fource, it is fuppofed that 

 Metius gained his information, as well as Cornelius Drcbell, 

 of Alcmaer in Holland, who afterwards made fimilar mftrii- 

 ments. We may alfo mention Francis Fontana, an Italian, 

 as one who claimed the honour of this invention in the )ear 

 1608 ; but from what we have already faid, of Janfen par- 

 ticularly, he cannot be confidered as the firft inventor, 

 though it is poffible that the report of fuch an invention 

 having taken place might incite him to devife the means of 

 eft^ecling a fimilar contrivance. This, it is generally undcr- 

 ftood, was the cafe with the famous Galileo, who, when 

 profeftbr of mathematics at Padua, heard it reported at 

 Venice, in the year 1609, that a Dutchman had prefcntcd 

 count Maurice of Naftau with an optical inftrument, whicli 

 had the property of making diftant objetfs appear as 

 though they were near ; but notwithftanding about twenty 

 years had elapfed fince the invention, the means ufed for 

 producing the wonderful effeft were not known ; and Galileo, 

 on his return to Padua, in a very few days not only contrived 

 but conftrufted a telefcope, which he prefented to the doge 

 Leonardo Donati, and to the fenate of Venice, together with 

 an account of the conftruftion and ufes which the inftru- 

 ment might be apphed to, both by fea and land ; for wlii^i 

 fervice it is well known that his ftipend as profeftbr was 

 thenceforth tripled. Among other difeoveries that were 

 made with Gahleo's telefcope in the heavenly regions, the 

 four fatellites of Jupiter were found by him to revolve round 

 this planet in their refpeftive periods, and were called tlie 

 Medkeanjlars, in honour of the houfe of Medici. This dif- 

 covery took place early in the year 16 10, and Gahleo, pur- 

 fuing his favourite ftudy till March, pubhftied at Venice his 

 " Nuncius Sidereus," containing an account of all his difeo- 

 veries, and dedicated it to Cofmo, the grand duke of Tiif- 

 cany, who, in a letter written by himfelf, invited the aftro- 

 nomer to quit Padua for an increafed ftipend, without the 

 labour of a Icftureftiip. The firft telefcope which Galileo 

 conftrufted had only a power of three times ; liis fecond was 

 fix times more powerful ; and his third magnified thirty- 

 three times, which, at fo early a date, was no contemptible 

 inftrument. 



Hence Galileo, though evidently not the firft maker of 

 a telefcope, has been confidered as entitled to all the merit 

 that is due to fuch a noble invention, feeing he had no model 

 before him, nor inftruftions how to proceed in the accom- 

 pliftiment of his ingenious work. But though Gahleo was 

 fuccefsful in the conftruftion and ufes of his telefcope, which 

 was of the refrafting fort, with a concave eye-glafs, as we 

 (hall ftiew prefently, vet it remained for that fagacious ma- 

 thematician Kepler to explain, on philofophical principles, 

 the ratioihilr of that conftruclion. It was he who firft ex- 

 plained the nature and effefts of both the converging and 

 diverging rays of light, after pafting through the refpeftive 

 lenfes, and who demonftrated the principles by which new 

 arrangements might be made in the glaftes, that would pro- 

 duce a fupcrior inftrument. He ftiewed that in fmall obli- 

 quities of incidence, the angle of incidence exceeds the angle 

 of refraftion about three times. 



Ff He 



