ERA ERATOSTHENES, 



83 



parts of soda are made up of 33 sodium and 11 

 oxygen. 



4. The quantity of any substance required to 

 decompose a given quantity of another, by simple 

 elective attraction, is at once taught by the scale. 

 Thus, if we wish to know the smallest quantity of 

 sulphuric acid adequate to decompose 100 parts of 

 chloride of sodium, by bringing 100, on the slider, 

 opposite to chloride of sodium, or its equivalent 60, 

 we find 665, on the slider, opposite to 40, the equi- 

 valent of dry sulphuric acid, and opposite to 49, the 

 equivalent of sulphuric acid of commerce, we find 

 81^ of the latter. We must, therefore, employ 665 

 of the former, or 8l of the latter. Again, to know 

 the quantity of dry sulphate of soda which would 

 result if all the common salt were decomposed, we 

 shall find 120, on the slider, opposite to the dry 

 sulphate, or to its equivalent, 72, and 270 opposite 

 to the crystallized sulphate, or to its representative 

 number, 162. 



5. The quantities of salts, each consisting- of two 

 ingredients, that are required for mutual decomposi- 

 tion, may be learned by a similar use of the sliding 

 scale. Supposing, for instance, that we have 83 

 parts of sulphate of potash, and wish to know the 

 quantity of chloride of barium required for their 

 decomposition ; bring 83, on the slider, opposite to 

 sulphate of potash, or to 88, its representative, and 

 opposite to 106, the equivalent of chloride of barium ; 

 we find 100 on the slider, which is the number 

 required. The results of this decomposition may 

 also be learned by examining the instrument when 

 in the same situation of the slider ; for opposite to 

 the equivalent of sulphate of barytes, 118, we find on 

 the slider 111, and opposite to chloride of potassium 

 we find 71.5 on the slider, the two last numbers indi- 

 cating the resulting quantities of the new compounds. 

 Again, from the weight of a precipitate, it is easy to 

 deduce the quantities of salts which have afforded it. 

 Thus, if we had obtained by experiment 120 parts of 

 dry sulphate of barytes, on bringing that number 

 opposite to its equivalent, 18, we see at once that 

 they may have resulted from 89g of sulphate of pot- 

 ash, and 108 of chloride of barium ; and moreover, 

 tliat 120 parts of barytic sulphate are composed of 

 40-6 sulphuric acid, and 79-4 barytes ; the sulphuric 

 acid consisting of 16-5 sulphur and 24-1 oxygen, and 

 the barytes of 8.15 oxygen and 71*25 barium. 



Other applications still, of the scale of chemical 

 equivalents, are pointed out by doctor Wollaston in 

 his memoir, explanative of its principle and uses, in 

 the Phil. Trans, for 1814 ; but the accurate and 

 ready solution of so many important practical pro- 

 blems as have been noticed above are sufficient to 

 show its importance to the chemist. Doctor Ure 

 remarks of it, that it is " an instrument which has 

 contributed more to facilitate the general study and 

 practice of chemistry than any other invention ol 

 man." 



ERA. See Epoch, and JEm. 



ERASMUS, DESIDERIUS, a celebrated scholar, was 

 born at Rotterdam, in 1467, being the illegitimate 

 son of a Dutchman of Gouda, by name Gerard, and 

 the daughter of a physician. He was a singing-boy 

 in the cathedral of Utrecht till his ninth year, then 

 entered the school at Deventer, where he displayed 

 such brilliant powers, that it was predicted that he 

 would be the most learned man of his time. After 

 the death of his parents, whom he lost in his four- 

 teenth year, his guardians compelled him to enter a 

 monastery ; and at the age of seventeen, he assumec 

 the monastic habit. The bishop of Cambray deliv- 

 ered him from this constraint. In 1492, he traveller 

 to Paris, to perfect himself in theology and polite 

 literature. He there became the instructer of severa" 



ich Englishmen, from one of whom lie received 

 i pension for life. He accompanied them to Eng- 

 and in 1497, where he was graciously received by 

 he king. He returned soon after to Paris, and then 

 ravelled into Italy to increase his stock of know- 

 edge. In Bologna, where he received the degree 

 f doctor of theology, he was one day mistaken, on 

 iccount of his white scapulary, for one of the physi- 

 ians who attended those sick of the plague ; and, 

 iOt keeping out of the way of the people, as such 

 >ersons were required to do, he was stoned, and nar- 

 owly escaped with his life. This accident was the 

 iccasion of his asking a dispensation from the vows 

 of his order, which the pope granted him. He visited 

 Venice, Padua, and Rome ; but, brilliant as were 

 the offers here made him, he preferred the invitation 

 of his friends in England, where the favour in which 

 le stood with Henry VIII. promised him still greater 

 advantages. When he visited the lord chancellor 

 sir Thomas More without making himself known to 

 lim, the chancellor was so delighted with his conver- 

 sation, that he exclaimed " You are either Erasmus 

 or the devil." He was offered a benefice, but was 

 unwilling to fetter himself by an office of this kind. 

 Hie was for a short time professor of Greek at Ox- 

 ford. He afterwards travelled through Germany 

 and the Netherlands, and went to Bale, where he 

 tiad his works printed by Froben. He died in 1536. 

 His tomb may be seen at Bale, in the Calvinistic 

 cathedral. 



To profound and extensive learning-, Erasmus 

 joined a refined taste and a delicate wit. Naturally 

 fond of tranquillity and independence, he preferred 

 the pleasure of literary ease and retirement to the 

 pomp of high life. His caution and worldly prudence 

 offended many of the best men of his times. He did 

 great and lasting service to the cause of reviving 

 learning. Although he took no direct part in the 

 reformation, and was reproached by Luther for luke- 

 warmness, he attacked the disorders of monkery and 

 superstition, and everywhere promoted the cause of 

 truth. He wished for a general ecclesiastical coun- 

 cil, to be composed of the most learned and enlight- 

 ened men, but did not live to see his wish accom- 

 plished. He therefore confined his efforts to serve 

 the world by his writings, which will always be prized 

 for their interesting matter and graceful style. The 

 best edition is by Le Clerc, Leyden, 1703, 10 vols. 

 fol. His life has been written by Burigny. Jortin's 

 life of Erasmus is a valuable work. Besides his 

 editions of various classics, and his other philologi- 

 cal and theological writings, we will only mention 

 his well known book in praise of folly (Encomium 

 Morice), and his colloquies. His letters are very 

 valuable in reference to the history of that period. 



ERATO (from ioa.a, I love) one of the muses, 

 whose name signifies loving, or lovely. She has 

 much in common with Terpsichore the same attri- 

 butes, the same dress, and frequently a lyre and 

 plectrum. She presides over the songs of lovers, 

 and touches, as Ovid, in his Art of Love, informs 

 us, the hearts of the coldest maidens by her tender 

 lays. See Muses. 



ERATOSTHENES, a learned man in the times 

 of the Ptolemies, born at Cyrene, in Africa, B. C. 

 275, was librarian at Alexandria, and improved the 

 science of mathematical geography, which he cor- 

 rected, enlarged, and reduced to system. He gained 

 his greatest renown by his investigations of the size 

 of the earth. He rendered much service to the science 

 of astronomy, and first observed the obliquity of 

 the ecliptic. (See Ecliptic.) Of his writings, one 

 only remains complete, Cataslerismi, which treats 

 of the constellations (Schaubach, with a commentary, 

 1795). Of his geographical works, which were long 



