25 Now since all this springs necessarily both from the nature of the principles of Christian revelation, and from the intrinsic properties which Our Apostolate should have, you see clearly, Venerable Brethren, how mistaken are those who think they are doing service to the Church, and producing fruit for the salvation of souls, when by a kind of prudence of the flesh they show themselves liberal in concessions to science falsely so called, under the fatal illusion that they are thus able more easily to win over those in error, but really with the continual danger of being themselves lost. The truth is one, and it cannot be halved; it lasts for ever, and is not subject to the vicissitudes of the times. "Jesus Christ, today and yesterday, and the same for ever" ( Hebr . xiii. 8).
Source: Iucunda Sane (Vatican.va)