1* 



MICROMETER 



was darned in UM ' Parentalis,' |>. 214, for Sir Christopher Wren, 

 on the ground ol communication which he nude to the Royal 

 SocMty in IMi. UM Journals of which society for October in that year 

 rwurd tbat " Doctor Wren inuaentul BOOM cuU, done by hiniK-lf in a 

 new way. wbrrrby he could almost M eoon do a mibjcct upon a plate 

 ol brass or copper at another could draw it with a crayon upon paper.' 

 Thu claim U howerer djapceed of by the fact that the principal mezzo- 

 Unto by Prince Kupert. the ' Decollation of St. John the Baptist,' after 

 a design by Spagnoletto, bean date 1858, which U four yean earlier 

 than Sir Christopher Wren's communication to the Royal Society; 

 whilrt Evelyn's Mcalptura ' (Svo, 1662), in which Rupert's " invention " 

 U deaeribed and illustrated by an engraving executed by the prince, 

 was presented to the Royal Society at the meeting of the 1 1th of Juno, 

 IMS, or four montha prior to Wren's communication. (Weld, ' Hist. 

 of Royal Soc., 1 1.118.) 



But while it U thus clear that the protenitlons of Prince Rupert 

 completely supersede those of Sir Christopher Wren, it is certain that 

 those of Prince Rupert himself are invalid. 



The real inventor of this art appears to hare been Louis von Sicgcn 

 (born 1609), a licutcnant-o-lonel in the service of the Landgrave of 

 He*** Ousel ; and according to Baron Heneiken (' Idee Ufoorale d'une 

 Collection Complete d'Estaiupes,' 1771), Prince Rupert learnt the art 

 from Von Siegen, whose first specimen made public was a portrait of 

 the Princess Amelia- Elizabeth of Hesse. Proofs of this engraving of 

 the first state bear the date 1642; of what ia called the second state 

 of which there is a fine impression in the Print Room of the British 

 Museum the date is 1043, which is //(em year* anterior to the earliest 

 of Priiice Rupert's dates. In the same collection there ore other prints 

 by Von Siegen, one of which, if the external evidence were insufficient, 

 would, we think, place the question beyond dispute ; for, although 

 without a date, it bears conclusive internal evidence of having been 

 produced in the very infancy of the art, since it exhibits a total mis- 

 conception or misapplication of its peculiar local powers, which, as we 

 have said, are especially calculated for large masses of shadow of an 

 indefinite character, such as a plain background to a portrait. The 

 work to which we allude, which is a portrait of the Princess of Orange, 

 the eldest daughter of Charles I., is a mixture of line-engraving and 

 mezzotinto, and in it the background (which, if the mixed stylo be 

 used, would be best effected by the mezzotint ground) is performed 

 wholly in cross-hatches by the old process; while the flesh and even 

 the hair, in which line-engraving might have been applied with advan- 

 tage, are produced wholly by the new process of mezzotinto. Von 

 Siegen's known mezzotinto plates are, we believe, in all only seven in 

 number. There are also works by Theodore Caspar Fiirstenburg, who 

 probably learnt the art from Von Siegen, which bear date 1656, being 

 earlier than anything by Prince Rupert ; but the works both of 

 Fiirstenburg and Prince Rupert are engraved entirely by the 

 newly discovered process of mezzotinto, and evince a more matured 

 knowledge of its powers than those of its inventor Von Siegeu. We 

 will only further add the remarkable fact, that ,Von Siegen frequently 

 attached the word " inventor " to his works, of which we subjoin an 

 instance in the inscription to a ' Holy Family,' engraved by him after 

 Carracci, and one of his latest performances : " Enunentiasitno I'rincipi 

 Domino D. Julio Mazzarini, S.K. K. , Cardinal!, &c.,novi hujus Sculptur.c 

 modi prim*! inraifor Ludovicus ;i Sicecn humilistfime offert client ct 

 oonsecrmt, A 1657." 



It U not improbable, however, that Prince Rupert by himself or 

 with the assistance of Wallerant Vaillaint, an artuit whom he retained 

 in his suite, may have improved the mechanical mode of laying the 

 BMtzotinto ground; and it should also be stated that thereu by Sir 

 Christopher Wrn a bead of a blackamoor, which is thought to have been 

 done by a process differing from that of Prince Rupert But these 

 observation, relate not to the principle of the art, but merely to the 

 tool with which the ;,n,um/ U produced. The more perfect instrument 

 at present uned (that is, the cradU) is said by Bartsch to have been 

 Invented by Blooteling. a very skilful engraver in menzotinto, who 

 produced many of bis works about l.;r_'. 



U is in our on country that mezzotinto engraving has been carried 

 to the greatest perfection, and it attained excellence early in the last 

 century. It was the favourite mode of Sir Joshua Reynolds, for whose 

 tyk iU painter like breadth was singularly well fitted, and his patronage 

 called forth a school of engraven who at once exhibited the fuB oapV 

 h^L ^"^ * their way can be derirtd than 

 the long serin of print* after Reynolds by James IC'Ardell, Fisher 

 Dkkion, RicJ-rT Hou*m, Valentin. Green, and * Tw.Uo 

 ^homas, Jamw, and Caroline) ; while, in a somewhat different way, 

 Jchard Earlom contributed more perhaps to the improvement and 

 extension of thw art than any one else, and whose works, embracing 

 te,! "ubject (hirtory, portrait, still life, &c.>, are iu 

 >''oUn of importance in the country. The superiority 

 ** E"B'-* oUnto engraver, has bn weQ 





<* to the prent day, when, inSr. Cousins, and other. 

 "**. Wntjr, we posMsi artisU without equal* among 

 for%ur in this branch of art. 



^ L 



' 



arUing 



subrtanoe., 



ftored to d-ip-te a certain volatile deleterious 

 ther from the bodies of the sick, from animal or 

 , or from th. earth, and capable of exerting a 



morbid influence on those exposed to its action. To the terrestrial 

 emanations the Italians have given the name of malaria (from mala 

 and aria, l*d air), and this word has been generally adopted into other 

 languages. To those emanations which arise from the bodies of the sick, 

 the term contagion is more properly applied. In common parlance, tlu-n, 

 miasma ia seldom employed to designate the contagious effluvium of 

 disease, but, with the adjunct marsh, is restricted to the sense in 

 which malaria is used : hence we speak of marsh miasma and malaria 

 as on* and the same thing. Though marshes, whether salt or fresh, 

 are prolific source! of malaria, they ore by no means the only sources ; 

 the mud which is left by the drying of extensive ponds and lakes, the 

 half-wet ditches of fortifications, and neglected sewers and drains, are 

 capable of furnishing this poison. The decomposition of vegetable 

 matter, in other circumstances than hi connection with soil, is likewise 

 capable of producing it; this has been exemplified in the sidelines* of 

 ships from the leakage of sugar into a damp hold. Having enumerated 

 some of the sources of miasma, the question naturally suggests itself, 

 What are the conditions essential to its development ? The mere namu 

 of marsh miasma suggests the idea of stagnant water, and if the pre- 

 ceding enumeration of circumstances under which the production of 

 malaria takes place be examined, it will be found tliat vegetable matter 

 and moisture are present in all the examples, and that animal matter ia 

 so occasionally. But how great soever may be the share which ni< 

 has in its production, it U certain th.it only a very small proportion is 

 necessary. A marsh, the whole surface of which ia thoroughly 

 comparatively innocuous ; but if partially or entirely dried by the 

 summer's heat, it becomes extremely pestilential in autumn ; 

 malaria, in its most intense degree, has been met with in low lands 

 which had become as dry as a brick ground, with the vegetation utterly 

 burnt up, and hence a high temperature seems to be another agent 

 necessary, or at least favourable to its development. According to 

 Dr. Ferguson, the only condition indispensable to the production of 

 marsh miasma on all surfaces capable of absorption, is the paucity of 

 water where it had previously recently abounded, a rule to which he 

 assures us there is no exception in climates of high temperature. ' if 

 the chemical and physical properties of malaria nothing is known ; even 

 the very obvious question, whether it is always the same kind of poison, 

 or whether a multiplicity of such poisons may not exist, is one whieh 

 the present state of our knowledge doea not enable us to answer. The 

 occasional existence of putrefaction in conjunction with malaria ia on 

 accidental concomitant, but by no means essential to its activity as a 

 poison. With regard to the effects of malaria, those manifest them- 

 selves in a longer or shorter period after exposure to its iufluen< 

 consist chiefly in the production of intermittent, remittent, and yellow 

 fevers, dysentery, and typhus. The long-continued application of tlio 

 same poison in a diluted form gives rise to various disorders of minor 

 import, gradually undermines the constitution, and produces premature 

 old age ; even the inferior animals and vegetables partake of the ; 

 depravation which characterises malarious districts. The most efficient 

 means of preventing the generation of the malarious poison, an.l, liy 

 consequence, the diseases to which it gives rise, are, the draining of 

 swampy lands, and preventing the accumulation of putrid or putrescible 

 vegetable or animal matter. 



MIUIAKI..MAS, the feast of St. Michael the. archangel, 20th of 

 September. Brady says it was first established in A.D. 487. Michaelmas- 

 day is oue of the regular periods, in this country, for settling rents ; 

 and an old custom is still in use of having a roast goose to dinner on 

 that day, probably because geese ore at this time most plentiful an.l in 

 the highest perfection. There were formerly many superstitious con- 

 nectea with the observance of this day. 



( I! > , Sir II. Kllis's edit,, 1841.) 



MICKo.MKTKK (from /c*(>it unaH, and nirpoy a meature), the 

 term generally applied to contrivances for measuring small spaces or 

 angles with great accuracy or convenience. 



The word is not applied to some artifices for subdividing the gradua- 

 tions of on astronomical instrument (for these see VI;HMI:K), nor when 

 a magnified portion of a subsidiary arc is used, which may be best con- 

 sidered under the heads of SECTOR, and 7.\ .-, n n Sirrou, though they 

 come properly under the definition. We shall follow the usual mean- 

 ing of the term. 



J. I IV--, Micrometer. When the rays from any bright object fall 

 upon a convex lens, an inverted image of the object is fanned, which 

 may be viewed by the eye-piece as if it were a material body. If a 

 fine wire or spider's web bo stretched across the telescope tube at the 

 place where the image is formed, this too will be seen diet 

 through the eye-piece. Instead of fixing the wire to the telescope tube, 

 it i stretched across a sliding-piece, which is moved bv a screw perj>en- 

 dicularly to the length of the telescope, and can thus be made to 

 measure the image in terms of the revolutions and parts of the 

 The head of the screw is divided, and there is an index by which the 

 part* arc read off. A little tongue passing over the notches of a plate 

 notes the whole number of revolutions. 



An Kngli-li gentleman named (jatwoigne seems first to have applied 

 nciplo to practice, but he unfortunately lost his life, in 1014, in 

 the great civil war ; and though his telescope fell into Townley's hands, 

 and was used by him, the construction doe* not seem to have been 

 generally known until it was re-invented by Auzout in 1666. Different 

 improvements were gradually mode nearly up to the present time. 



