Fort Sinith, Ark., Jan. 6. Liout. W. A. Brittain, oí King's Third Arkansas regiment of Fagou's rebel brigade, carne nto our Unes to day ith a squ.id ofhw command. Ho left Prive's headquartors at Seilgwood, tn'eivty. inüuá west of Cuiden, in Christin as Gen. .Ilolinea ig in cotnm-'uid of the Mississippi Department. Priue commando the army in the tild, which is esiimated at 17,000 strong, but Brittain -says tho entire efftelive rebol forcé, outside of Texas, don 't uxceod 13,000. Of Pricu's Misourians ouly abuufc thrce or four thouHtind reuiain, and ih t a few of ttiese are part of tho anny ie took out of Missouri. The veterana of Lexington and Pea líidíje are neaiiy uil in theii graves. Tlie Missouri troops are Sholby's cavalry and Paison"s infantry brigado, Mosby'e new reoruit, conncripls aud bushwhuckers, who recenlly joined. General Steele has been euperseded in command of the rebel department of; lhe Indian Territory by Brigadier General Maxy. General Gano is another new Texan General who has had command. The rebel troops havo iasuoa of only frosh beef and corn rneal, vvith one ration of ñour per weet. They are budly clothod, have no tents and öad suffer greiitly. Keports of Federal miccesses in Texau-, and Banks' posesosion of Richraond, creatud great gioom aitiorig tho rebels. iiumors of the issuo of President Liucolu'a aranesty proclaination also liaving an effect throughout the'r rnnks, and deserlionw wcre f'rexuont. Offiuora were pro:nising the men speed v advanue Northward, to kaop them qniot. Many well informud oiFiccrs ware of opinión that Prico wotild move with his column pon Little Rock, and Mux"fc vvith another, on Fort Smith. ïha weather here is the coldeat evor known. The tliermometer has stood from 10 to 15 deg. below zuro for sev. eral daya. Suow is ix inches deep. The oavalry crossed the river on the iee and iutercepted the rebel mail. Lettors spaak of an immediate advanco of thair forcea northward n irobabio.