Mr. A G. Brown, formerly a Sonator in Gongress from Mississippi, and doït a Confedérate Senator at Richmond frorn the sarao State, lias written a letter to the Ricbmond Enqiúrtr of the 13tli, in reply to a oommunication that appeared charging tho Federal governmetit with maltreating the rebt'l prisoners 011 Johuson's Island. Mr. Brown ssiys he has a fríend there who corresponds wilh him regu'arly, and sajs his imprisonment was as mild as he could expect, and that he was in want of DOthing hut liberty. - VVitli regard to fnel, Mr. Brown says his correspondent tells hun the prisouers hav a sufficiency, and (says Mr. Brown) "on the I2th he givos a bilí of prisoi) faro, and I undertake to siy that half the families in iiiehniond do not ftire so well." Again, tho correspondent says: "My life would bo very eudurable were I not a prisonor." Mr. Brown says ho does not know wliy thia officer shouid be trentcd. botter tiian any other, and "beides, in speakiog of the treatnient ol' the prisoners, he eoustantly uses the word 'ue '" Mr. Brown States his reasona for making i his afatement thus: "First, I would Jo justico to an eijeray; riext, I would not exaspérate that enemy by publisbkig eiffggerated it not falae accounts of his cruel treatment oí' our prisonei's, and thus induce hiui to chongo mild and oven kind treatment into har8h if not cruel treatment; and lastly, these accounts will meet ths eyo of many persons in onr country who have frienda ou Johnson's Island, and if uncorrected, they cannot fail to inflict unnecessary pain upon such persons. - With a change of oommanders thero may come a change of treatment, but I am perfeetly satis'ied that, up to tho 20th of lust month, the prisoners on Johusou's Island were treated as well as their friouds in the Confederacy could reasonably expect." Upon thia letter tho Enqxúrer comment s, and makes an issue between .Teff. Davis and the Senator by saying that f the statements made as to ill treatment of rebel piisoners by corrcspoudeiits were falae, then also President Davis made a "falso statement" when he in In uiessuge ealled attention to the alleged ill treutment of rebel prisoners on Johnsou's Ia land. Brigadier General K. S. Howe, lately comniunding a división of tho Sixth Corps, lina been transí'erred to tho post of Chief of Artillery, vire Brigadier General Barry. ordored to Gen. Grant's department. Gen. Howe has been in the field unintcrruptedly from the begiuning of tho war, and is regarded as a most acconiplished oiEecr. ïhe WorU states that the rebel War Department has set on foot nieasurcs to conscript 20,000 negroos to work on forti ficstions at llichnjond auJ elsewhere.