The new Commission of Architects to examine the Chicago Custom House arrived there at the close of last week. A Washington special says of their instructions : " They will devote theniselves exclusively at first to the sturty of the foundation, and will make practical tests of their capability to bear the weight of the propostd building. This will be done'by the erection of a reservoir upon the weakeat portion of the foundation, with a view to ascertaining if it is able sustain a weight of water equivalent to the estimated weight of the walls whe.n compk'tod. If the use of water in this mauser is not found advisable bags of sand will be used. If the foundations are found to be sound the charaoter of the stone will be exaiuined into. If the walls are found not to be secure the commission will Heek to determine upou souie method of securing them and estímate thu coat."