【正文】 and sol ve thi s probl em . H e knew that chol era woul d never be control ed until i ts cause was found. H e becam e i nterested i n two theori es that possi bl y expl ained how chol era kil l ed peopl e. The fi rst suggested that chol era m ul ti pl i ed i n the air. A cl oud of dangerous gas fl oated around until i t found i ts vi ctim s. The second suggested that peopl e absorbed thi s di sease into their bodi es wi th thei r m eal s. From the stom ach the di sease qui ckl y attacked the body and soon the affected person di ed. John Snow suspected that the second theory was corect but he needed evi dence. So when another outbreak hi t London i n 1845, he was ready to begi n his enqui ry. As the disease spread qui ckly through poor nei ghborhoods, he began to gather i nform ati on. In two parti cul ar streets, the chol era outbreak was so severe that m ore than 500 peopl e di ed i n ten days. H e was determ i ned to fi nd out why. Fi rst he marked on a m ap the exact pl aces where al the dead peopl e had l i ved. Thi s gave him a val uabl e cl ue about the cause of the di sease. Many of the deaths were near the water pum p i n Broad Street (especi al y num bers 16, 37, 38 and 40) . H e al so noticed that som e houses (such as 20 and 21 Broad Street and 8 and 9 Cam bri dge Street) had had no deaths. H e had not foreseen thi s, so he m ade further i nvesti gati ons. H e di scovered that these people worked i n the pub at 7 Cam bri dge Street. They had been gi ven free beer and so had not drunk the water from the pum p. It seem ed that the water was to bl am e. Next, John Snow l ooked i nto the source of the water for these two streets. H e found that i t cam e from the ri ver pol l uted by the di rty water from London. He i mm edi atel y tol d the astoni shed peopl e i n Broad Street to remove the handl e from the pum p so that it coul d not be used. Soon afterwards the di sease sl owed down. H e had shown that chol era was spread by germ s and not i n a cl oud of gas. In another part of London, he found suporti ng evi dence from two other deaths that were li nked to the Broad Street outbreak. A wom an, who had m oved away from Broad Street, li ked the water from the pum p so m uch that she had i t deli vered to her house every day. Both she and her daughter di ed of chol era after dri nki ng the water. Wi th thi s extra evi dence John Snow was abl e to announce wi th certai nty that pol l uted water carried the vi rus. To prevent thi s from happeni ng agai n, John Snow suggested that the source of al the water suppli es be exam ined. The water pani es were i nstructed not to expose peopl e to pol uted water any m ore. Fi nal y “Ki ng Chol era” was defeated. COPERNICUS’ REVOLUTIONARY TH EORY N i col aus Coperni cus was fri ghtened and hi s m i nd was confused. Al though he had tried to ignore them , al hi s mathem atical cal culati ons l ed to the sam e concl usi on: that the earth was not the centre of the sol ar system. O nl y i f you put the sun there di d the m ovem ents of the other pl as i n the sky m ake sense. Yet he coul d not tel anyone about his theory as the powerful Chri sti an Church woul d have punished him for even sugesti ng such an i dea. They beli eved God had m ade the worl d and for that reason the earth was speci al and m ust be the centre of the sol ar system. The probl em arose because astronom ers had noti ced that som e pl as i n the sky seem ed to stop, m ove backward and then go forward in the loop. O thers appeared bri ghter at ti mes and l ess bri ght at others. This was very strange i f the earth was the centre of the sol ar system and al pl as went round i t. Coperni cus had thought l ong and hard about these probl em s and tri ed to fi nd an answer. H e had col ected observations of the stars and used al l his m athem ati cal knowl edge to explai n them . But only hi s new theory coul d do that. So between 1510 and 1514 he worked on i t, gradual y im provi ng hi s theory until he fel t i t was pl ete. In 1514 he showed i t pri vatel y to hi s fri ends. The changes he m ade to the ol d theory were revol uti onary. H e pl aced a fi xed sun at the centre of the sol ar system with the pl as goi ng round i t and only the m oon stil goi ng round the earth. H e al so suggested that the earth was spinni ng as it went round the sun and this expl ai ned changes i n the movem ent of the pl as and i n the bri ghtnes of the stars. Hi s fri ends were enthusi asti c and encouraged him to publi sh hi s i deas, but Coperni cus was cauti ous. H e di d not want to be attacked by the Chri sti an Church, so he onl y publ i shed i t as he lay dyi ng i n 1543. Certai nl y he was ri ght to be careful. The Chri sti an Church rejected hi s theory, sayi ng i t was agai nst God’s i dea and peopl e who supported i t woul d be attacked. Yet Coperni cus’ theory i s now the basi s on whi ch al our i deas of the uni verse are bui l t. Hi s theory repl aced the Chri sti an i dea of gravi ty, whi ch sai d thi ngs tel l to earth because God created the earth as the centre of the uni verse. Coperni cus showed thi s was obvi ousl y wrong. N ow peopl e can see that there i s a di rect l i nk between his theory and the work of Isaac N ewton, Al bert Ei nstei n and Stephen H awki ng. Uni t 2 PUZZLES IN GEOGRAPH Y Peopl e m any wonder why di fferent words are used to descri be these four countri es: England, Wal es, Scotl and and N orthern Irel and. You can cl ari fy thi s questi on i f you study Bri ti sh hi story. Fi rst there was Engl and. Wal es was li nked to i t i n the thirteenth century. N ow when peopl e refer to Engl and you fi nd Wal es i ncluded as wel l. N ext England and Wal es were joi ned to Scotl and in the seventeenth century and the nam e was changed to “Great Britai n”. H appi l y thi s was ac pl ished wi thout confl ict when King Jam es of Scotland becam e King of Engl and