It seems that immediately succeeding this year of remarkable health, in the course of the first half of the year 1852, "an unusually large number of cases of mental affection" occurred, which led to the substitution of brisk walking in concentric rings for exercise in separate airing yards--the abolition of the mask or peak which was found useless as a preventive of recognition, and the doing away of the chapel stalls. It is well known that these three features of the Pentonville system were designed to carry out the principle of strict separation. If they were found ineffectual for this purpose, their abandonment is a matter of no moment; and as the term of imprisonment in this penitentiary is regarded as probationary, and is moreover restricted to twelve months, we can scarcely suppose that such changes were required by way of relaxing the discipline. Colonel Jebb gives us to understand that the prejudices of the public against separate confinement are gradually subsiding, and he thinks it "of greater importance to the more general introduction of the system that every effort should be made to secure its great advantages without again raising the question of its safety." Is there no danger, however, that its efficacy may be so far diminished by needless relaxation, as to make it scarcely worth the trouble of introducing it? We have not a shadow of evidence, nor even an intimation that the supposed increase of insanity was in the slightest degree the result of severe discipline; nor have we any report from the medical officer, visiting or resident, as to the existence of such "an unusually large number of cases of mental affection." But whether they existed or not, "they were believed to exist," and the Board of Commissioners directed the changes to which we have above adverted. In the progress of the inquiries on the subject, it was suggested to the visiting director, that he should obtain the joint opinion of the Governor, Chaplain and Medical Officer on sundry points, among which were the following: 1. Whether it appears necessary to reject any particular description of prisoners as being unfit subjects for separate confinement, such, for instance, as those of dull intellect, or others who do not speak the language, and are, therefore, less capable of instruction. 2. Whether the arrangements at Wakefield and Leicester, with regard to assembling for public worship, school instruction, exercise in association, &c., are likely to be the cause of a more favorable effect of separate (?) confinement on apparently the same class of prisoners. 3. Whether a greater stimulus or a greater degree of vigor cannot be imparted to the trades and occupations in the cells.