SAINT LOUIS, MO., July 8, 1864.

Colonel J. P. SANDERSON, U. S. Army:

SIR: I have the honor to state that I arrived in this city to-day at 9. 30 a. m. I desire to state, respectfully, that through I have literally filled my written instructions I have not had the time which was necessary to devote to certain localities. I devoted too much time to Cincinnati. I was under the impression that this organization was in full force there, and only required perseverance to develop it. This I regard now as a mistake; I was satisfied of it before I left there, but confirmed in my belief from what I learned in Hamilton, Ohio. When I left here I presumed I could fill my instructions in one month, and this I should have done had I devoted less time to Cincinnati. Shortness of funds compelled me to neglect Detroit, Mich.

I do not pretend to know what your intentions are for the future regarding this secret organization, but in returning I cannot refrain from offering you the result of my experience on a few important points. To be fully effective in ferreting out the secrets of this organization a man should cover his true object by some ostensible business. If he were only engaged as an agent for some popular paten, or a gambler, it would afford him an immense advantage. Another thing that I will venture to say is this: If you wish to keep a knowledge of what this organization is doing in the future, from what I know of its workings I incline to the belief that a man can form a better view of what it is doing, as a whole, from taking up a residence at some particular point than he can by traveling from point to point and laboring under the embarrassments of a stranger. He would soon gain full confidence, and if he did not engage in correspondence in all parts of the country he would have access to that of those who did. Men in Hamilton know as well what the brethren in Springfield, Ill., are doing as what they are doing in Columbus. These observations are made from the interest I fell in thwarting the designs of these scoundrels, who are as much lower in my estimation than Quantrill, John Morgan, or Forrest ad his followers than Arnold is lower than Brutus.

I omitted to say in the proper place that I met in the cars this morning a man named Dailey, of Montgomery County, Ill. He is a "butternut. " He says his country is organized, and thinks Illinois is generally. Thinks she will resist the draft. He was running away from Illinois to missouri in consequence of indictments for selling liquor without license. He was going near Saint Joseph, Mo.

I also met a man named Joe Butler, who hails from Vicksburg, Miss., and is a professed rebel. He has just been on a visit to his son, who is at schools at Philadelphia, Pa. He says he has a daughter going to school at Saint Charles, Mo. He is familiar with things in Missouri, especially in Saint Louis. He says he stops in Saint Louis with a friend named Kennedy, residing on Eighth street. Joe says there is great disaffection in Pennsylvania; says there will be great trouble not far in the future. There is a mystery about this man Butler, in my impression, which I have not the time nor opportunity to develop. He is a small man with dark or copper complexion, dark eyes (with a sort of cock or slant in the left eye), wears no beard, is lightly made, and has on gray clothing and old-style round-toed boots.

I have been in this city but a few hours, but I have been no place where I see the "Sons of Liberty" freer to converse with, or meet