[By Out Own Correspondent.] Speaking of the practical, reminds me of the boornerang. For moro than twenty years have I searched for thia extraordinary weapon. Ii my different trips to Iho oíd world, I aought it but, not hearing of it, nor eceing it, concludei it was a myth, and was used as an Ulustration by politicians. Sucli an one waa tising a boom erang - as we would say, ' ' hoiating one on hit own petard." It is said of this formidable weapon, that when hurled at an o' ject by a native it moves along just aboye the ground with great rapidity, and after reaohing ita objective point, leaps aa it were into mid air, and thus poiaed for the moment takea a rotrogresaive movement in an air line for the point from which it was cast, thus making it as dangerons to the thrower, if inexperienced, as a heavily charged blunderbuss. It has been as great a puzzle to the aavans and scientists as the ealculating machine of Babbage. Four of these curioua apecimens of savage genios are to be aeen in the department of Australia. There are seventy-two block and slab apecimens of timber from Sydney. They alao exhibit, ead dlea, wools, tweeda, and shawls, none of which will comparo with the American aection, an coal seams twelve f eet thick are shown as specimens from Hunter river district, northern coal fielda of New South Wales. There are aixty-six collieriea. They also exhibit preaerved meato, candlea, biscuits, condimenta ores of antimony and other minerals. In a glasa ahow caso fourteen feet square are shown, on one side, the prismatic compasa transit, sextant and other instrumenta nsed by that intrepid navigator, Lieut DeHaven, near the írigid wilds o Western Groenland ; drawings and paintinga of Arctic scenery and animal life, executed bbimaelf, and the flag of the Advance, the ship in which he made his second vqyage ; the threo other sidea of the case contain relica of tuo expeditious of Hayes, Hall and Bradford ; the flag that Wilkes took on his Antarotic ex pedition in the ship Peacock, the same fla being takou by Kane, llayes and Hall, alwo, 01 their Arctic yoyagea ; relica of Sir John Franklin's expedition, including portiona of his vee sel secured by Capt. Hall in his second expe dition and brought back by him then, together with relica of Parry'a voyage ; the journala kept by Hall in his Polaris expedition, and a fac similo of the sledge made for Capt. Hall bi "Esqnimaux Joe." Brazil haa $3,000,000 in diamonda to display, but the United States, requiring a persona bond in amount doublé the invoice from the Commission, has declined, henee we will not see the brilliants. The Bullock printing press priuta 32.000 copies per hour. The Portuguesa have a handsomo building one story high within, and two without. In the Bntish section there are eighty-five exhibitors of Chemicals, and fourteen oxhibitors of watchea and chronometers. The latter timepiecea were invented by John Amold one hundred years ago. The georama of Paris is aboutlO feetaquare, is exposed to the weathcr, and unless taken out of the wet, will be as the ' ' baseleas f abric of a visión." The Navy department of the United States, in the Government building, is arranged under nine heads: Ordnance, torpedoes, equipment, navigation, construction, yards and docks, medicine and surgery, provisiona and clothing, steam engineering anc naval observator? and Arctic relies. Japan exhibits two vanos six feet high anc thirty inches in diameter, price $2,000 gold, small vases ten inches high, $30 in gold. white and blue china goods far below the English Standard at fabulous prices; $50 in gold for a table wortü 10 or $15. I thought these figures of a bonanza charaoter, but when I saw a suii or 'ouckakin- coat, vest aud pants, trimmec with a few yards of BÜver lace, frota Mexico, price, $1,000 gold, I threw up the sponge. Blinde of thoAztecsand of Montezuma, where art ye? The bijouterie of Japan, their lacquered ware, and straw goods are superior, and many articlea are low enough, but, in their valuable articles, they are in the clouds. Tlie prices they aak would impoverish the Tycoon did he becomo a purchasor. In the Egyptian department $2,000 gold is askcd for a süver autique set, worth possibly a few hundred dollars ; a few pieces of sandál wood, $9 gold. If the Americana can stand these extortiona, they are specimeus of endurance to be wondered at. What do the readers of this letter think of a backgammon board, inlaid, $600 gold ? The Egyptiana have a aaored crocodilo with them to palliatc their excesses. I am happy to state he is atuffed. One watch factory, American, ahowa 2,200 watchea, representiug six days, of ten hours each, of the employés. A tack factory exhibits 2,000 varieties of tacks. Strawberries will be displayed Juno 7. Easpberries July 3. Peaches, grapea, nuts, coréala, honey and wax, mclons, horaes, cattle and poultiy will follow at different dates. In addition to Gilmore's coucerts, othor musical banda will perform in different parta of the main building. The French steamcr ljrought the French, Belgian and Ilussian Judges of Centennial awards, and á00 tons of French exhibits. There will be 5,000 free seats distributed tliroughout the grounds. Tropical frnits from Bermuda were shown on the 18th inst. Michigan and New York are in the front rank of apple-growers. The Committee on Conceesions havo determined to enforco contracts with restaurants, tho leading feature of which was fair prices. Oregon exhibits wheat reaped in ninety daya after sewiug in ground neithor plowed nor harrowed. It is said Queen Victoria will "put in an appcaranco " at the Exliibition. But few children as yot are aeen on the Exbibition grounda. The Netherlanda show carpeta from the oyal factory, which would fit a room eighteen 'feet pquare, $280, Haarlem shows a magnt of )ounds;prico$110. Rotterdam ilmplava an exteneighty-eight ponnds. carricB a woigbt of 500 ivo assortment of fisbiug tackio. Amsterdam, upen of tho quaintost JDulch stylo, georamas f cañáis, mapa, and a ewing donble-crane ridge, aud a ' georama of the stirf ace of the Zuyder Zoo. Bermuda has a pieco of a xanthoxylon. It was taken from a utnmp by a British soldier of '1. M. Fifty-third. It is of yellow wood, per'ectly sound, and dates back to 1(512. Aleo, 'rom the island, black mangrove, rubber, olive, fiddle and other woode. Arrowroot is a long, yollow-looking root liko tho horse radiah. The Ctntonnial stampod envelope is good anywhero in the United Staten. A ailvor brick ha arrived from Nevada 117 lounds in woight; valué in gold $1,(523.65. [ts aomething to be a "brick." The rednction of the admission fee is in déjate. As Horace Greeloy would havo said, " If yon aro going to reduce, why don't you reduce ?" Tho Middlo States peoplo are farming and can't come. It is too early for the WeBt and South. Waituntil Jitly, and then see the jam. Grand competition betwcen the chief military bands of America in tho Contonnial grounds July 5th. Details Will soon be arranged and published. It takes a general manager, ono captain and aid, chief clerk, a chief inspector, twelvO inspectora, 102 gate keepers, 2 special gate keepers, one chief and sixteon wagon gate keepers to pass the maases üi. An iron bank vault ia on exhibition, price Í25.000 : lOxlG feot, 14 feot high, weighs 35 tona, 4 doors and 20 bolts to oacn, lining steel, plate 2}4 inches, 2 feet of liling, iireproof. The ame makers put ono up in Baltimore 25x 35, weight 200 tons. Farrel & Co., show a piagniflcent circular aai e. A bcautiful display of ornamenta are exhibited from Florida. The American Bible Society. Res Di ved, "We endorse the action of tho Centennial CommisBionors in rofusiug to open the Exliibition on Sunday." Bartholdi and Rochambeau havo arrived, the former a famoua French architect, the latter the deBcendant of a stock whoae sympathics re with the Colonies in thoir struggle for independence. In spite of tho reporte tothe contrary, if you oan come to the Exhibition you wili find no difliculty in securiag comfortable quartera and at lew rates. If you wish rooms en-suite on first floor, and cali for pato do fois grae, with Cnambcrtin and Lafitte, you will find the bill as largo as if in Paris at the Mille Colon, or Vie Vofour or Troisfreres. The latter is branched hcre. J. B.