CONSISTENCY OF MATERIALS RELATED TO PHYSICAL MEASUREMENTS 55 to analyse their general judgements of consistency into separate physical components. We once asked a number of cheese experts, and others, to score a batch of cheese separately for firmness, springiness and crumbliness. There was little physical correlation between these properties among the samples given and the inexpert had, in general, no difficulty in giving us separate orders for the three. But the experts always gave the same order they could not get away from the combined concept of "body," which includes all that can be felt with the fingers. When we did get a number of separate subjective assessments of different rheological characteristics, as well as several physical tests, we generally sorted out the correlations, i.e. simplified the correlation matrix, by means of Multiple Factor Analysis but I have already described this technique to you in some detail (1). Just how the expert reaches his conclusions and interprets his sense data we do not know, but we used to think that such judgements are mainly concerned with kinaesthetic (joint and muscle) sensations rather than with cutaneous (skin) sensitivity. More recent experiments by Harper have, however, thrown some doubt on this conclusion. Much more work requires to be done. The rheologist, as a physicist, naturally likes his concepts and especially his definition of "physical properties" to come within the range of Continuum Theory. Properties should have well-defined dimensions, generally expressed in powers of mass, length and time, should be invariant to changes in coordinate systems, and so forth. Unfortunately, human beings do not judge consistency in these terms or if they do try to do so, they are attempting to bridge the gap between subjective and objective measurements in a somewhat artificial way. Fundamentally, my own view is that the gap is unbridgeable but I am also quite confident that physical measurements, whether of primary physical properties or of more complex behaviour, can most certainly help - but not replace the craftsman. The greatest difficulty facing those working in this field is to persuade the craftsman that this is so and that we are not secretly attempting to replace him by machines. (Received: 7th October 1964) ACKNOWLEDGEMENTS The author gratefully acknowledges permission by the following to reproduce the illustrations: The Royal Society for Fig. 1. The Editor, American Journal of Psychology, for Figs. 2 and d.

56 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The Editor, Nature, for Fig. 3. The Editor, British Journal for the Philosophy of Science, for Fig. 5. The Editor, Science, and Prof. S. S. Stevens for Fig. 6. REFERENCES (1) Scott Blair, G. W. J. Soc. Cosmetic Chemists 11 181 (1960). (2) Scott Blair, G. W. in Harrison, V. G. W. Some Recent Developments in Rheology (1950) (United Trade Press, London). (3) Stevens, S.S. Science 105 677 (1946). (4) Stevens, S. S. Chap. in Churchman, C. W. and P. Ratoosh 3/Jeasurement: Definitions and Theories (1961) (Chapman & Hall, London). (5) Sheppard, D. Brit. J. Psychol. 45 40 (1954). (6) Boring, E. C. A History of Experimental Psychology, 2rid Edn. (1929) (Appleton-Century- Crofts, Inc. New York). (7) Bergson, H. Essai sur les donndes immddiates de la conscience {transl. F. L. Pogson as Time and Free Will (1960) (Swan Sonnenschein, London). (8) Stevens, S.S. Psychol. Rev. {14 157 (1957). (9) Treisman, M. Brit. J. Philos. Sci. 15 130 (1962). (10) Treisman, M. Nature 198 914 (1963). (11) Treisman, M. Quart. J. Exper. Psychol. 1õ 11, 387 (1964). (12) Tannery, J. Correspondence in Revue Scientifique reproduced in Etudes Psycho- physiques by J. Delboeuf, Baillitre et Cie, Paris (1883). (13) Stevens, S.S. Quart. J. Exper. Psychol. 1õ 383 (1964). (14) Katz, D. Cereal Chem. 14 382 (1937). (15) Scott Blair, G. W. and Coppen, F. M. V. Proc. Roy. Soc. (B) lg8 109 (1939). (16) Scott Blair, G. W. and Coppen, F. M. V. Amer. J. Psychol. 55 215 (1942). (17) Harper, R. Amer. J. Psychol. õ0 554 (1947). (18) Scott Blair, G. W. and Coppen, F. M. V. Nature 149 22 (1942). (19) Nutting, P. G. Proc. Amer. Soc. Test. 3/Jater. gl 1162 (1921). (20) Scott Blair, G. W., Veinoglou, B.C. and Caffyn, J. E. Proc. Roy. Soc. (A) 189 69 (1947). (21) Scott Blair, G. W. and Caffyn, J. E. Phil. g/Jag. (ser. vii) 40 80 (1949). (22) Scott Blair, G. W. Brit. J. Philos. Sci. 11 272 (1961). (23) Dingle, H. Phil. g/Jag. 40 94 (1949). (24) Harper, R. and Stevens, S. Quart. J. Exper. Psychol. 16 204 (1964). (25) Stevens, S.S. and Guirao, M. Science 144 1157 (1964). (26) Oldfield, R. C. and Zangwill, O. L. Brit. J. _Psychol. $g 267 $$ 58 113 (1942).