PERHAPS it is desirable to explain that my review of Prof. Schuster's book published in NATURE of September 21 was written and sent to you before Prof. H. H. Turner had delivered his address to the British Association as president of Section A. Consequently, nothing in my review is a reply to, or has any reference to, Prof. Turner's excellent address. It would be discourteous to criticise an important pronouncement of a leader in science in any back-handed way. My statement and his are probably not really in opposition, though they to some extent emphasise opposite types of investigating activity.