But there was one regular visitor whose behaviour was more puzzling. This middle-aged man carried what looked like an ordinary wooden walking cane. If he came to a cage where the inmate was close enough, he would slide his cane between the bars until its tip was beside the animal鈥檚 ear.
Once it had grown accustomed to this intrusion, a careful observer would have seen the man give his stick a little squeeze, all the while keeping a close watch on the animal. Then he鈥檇 move on to the next cage and do the same thing again.
What the puzzled onlooker couldn鈥檛 have known was that the cane concealed an ultrasonic whistle. The aim of the manoeuvre was to find out if animals could hear sound at frequencies inaudible to humans. And the man wielding this unique instrument was Charles Darwin鈥檚 wealthy half-cousin, the scientist Francis Galton.
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EVEN Francis Galton鈥檚 most ardent admirers have to admit he has an image problem. That鈥檚 because Galton invented eugenics-both the idea and the word itself-and presided over the Eugenics Society. While harmless as a debating topic among intellectuals, the science of human improvement was later to have dire consequences, notably in the hands of the Hitler鈥檚 Third Reich.
Cousin Charles鈥檚 The Origin of Species sparked Galton鈥檚 interest in inheritance. His own compilation of the pedigrees of eminent men convinced him that heredity is the main determinant of intellectual ability. And his pioneering studies of twins reinforced the conclusion.
Galton was a true Victorian. So having demonstrated the importance of heredity, the right course of action was to put it to work. If men could reshape the world of inanimate objects, why not also themselves? Taking the Greek word eugenes, meaning well born, he created eugenics.
Although this is still Galton鈥檚 main claim to fame-and one he might well have been proud of-it鈥檚 wrong to suppose that eugenics was all he cared about. Galton was a polymath: a hangover from the age of the gentleman scientist who saw no reason to limit his attention to one facet of nature. He also had a dilettante streak that led him to jump from one line of enquiry to quite another in totally different areas of science and technology.
Galton began by studying medicine at Cambridge, then switched to maths. Later interests included statistics, fingerprinting and anthropometry-the precise measurement of the size and shape of the body. He invented a Sun-sighting device, spectacles for divers, an 鈥渁esthesiometer鈥� for measuring the sensitivity of the skin to touch, and a periscope for seeing over the heads of the audience in crowded lecture halls.
Sensory phenomena, including the way people respond to high-pitched notes, also captured his attention. He was intrigued by an old Dorset proverb, which claimed that no agricultural labourer over the age of 40 can hear a bat squeak. And he was convinced that 鈥渁 parcel of schoolboys might interchange very shrill and loud whistles quite inaudible to an elderly master鈥�.
A firm believer in measuring and counting, Galton decided to put figures to these observations, and also to investigate animal hearing. He devised what have become known as Galton鈥檚 whistles. Three of the original whistles survive in the Galton Collection at University College London. One, about 5 centimetres long, is made of wood; the other two are larger and made of metal. Later and more sophisticated models included a screw plug for changing the effective length of the whistle to adjust its pitch.
Galton disputed the view common among Victorians that women鈥檚 senses were invariably more acute than men鈥檚. Using his whistles he tested almost 900 men and women of various ages for their capacity to hear notes of between 20 and 50 kilohertz- although given the difficulty of calibrating the whistles the frequencies may not have been as precise as he claimed. Despite this, the study did show that the sensitivity of both groups dropped with age-but that women鈥檚 declined significantly faster.
His animal experiments began simply enough. 鈥淚 found [the whistles] to produce marked effects on cats, and made many experiments at a house where I often stayed, in which my bedroom window overlooked a garden much frequented by them. My plan was to watch near the open window and when a cat appeared and had become quite unsuspicious and absorbed, to sound one of these notes inaudible to elderly persons鈥� I noticed the quickness and precision with which these animals direct their eyes to the source of the sound.鈥�
Having honed his skills in cat-watching, it was time to move on to the zoo and test the cane-mounted whistle. The cane was hollow and connected to a length of rubber tubing beneath the handle. A firm squeeze of the tube produced a short blast on the whistle fitted into the tip of the cane. If an animal challenged in this way pricked up its ears, Galton concluded that it had heard the sound. 鈥淪mall dogs also hear very shrill notes,鈥� he reported, 鈥渂ut large ones do not. You may pass through the streets of a town with an instrument like that which I used in the Zoological Gardens, and make nearly all the little dogs turn round, but not the large ones.鈥�
Galton also suspected that certain insects might hear sounds of even higher frequency. Knowing that a gas less dense than air would raise the upper frequency limit of his whistles, he commissioned a truly hare-brained instrument, 鈥渁n apparatus with a small gas bag for hydrogen鈥nd an India rubber ball to squeeze to enable hydrogen to be used with the whistle鈥�. Perhaps not surprisingly, given the difficulty of carrying hydrogen around, Galton doesn鈥檛 seem to have published any findings from such experiments.
If Galton鈥檚 observations are to be trusted, the term 鈥渄og whistle鈥� as a label for all ultrasonic emitters is a misnomer. 鈥淥f all creatures,鈥� he wrote, 鈥淚 have found none superior to cats in the power of hearing shrill sounds. It is perfectly remarkable what a faculty they have in this way . . . You can make a cat, who is at a very considerable distance, turn its ear round by sounding a note that is too shrill to be audible by any human ear.鈥�
In truth, none of these experiments was among the most fruitful of Galton鈥檚 career. 鈥淚 tried [the whistle] at nearly all the cages in the Zoological Gardens,鈥� he wrote, 鈥渂ut with little result of interest, except that it certainly annoyed some of the lions.鈥�
Despite this disappointing conclusion, Galton鈥檚 whistles became standard equipment in many psychophysical laboratories until the advent of more reliable electronic sound generators.