Further Reading
Biographical books are often a good source of information about how scientists get and develop ideas. Research papers tend to leave these aspects out. Look for biographies of scientists in your field. Crease [8] gives ten short biographies of experiments in physics. Though some of them do not fulfill our criteria for experiments they are well worth reading.
ANSWERS FOR EXERCISES
6.1 See the discussion in the two paragraphs below the exercise.
6.2 To express a causal relationship, a sentence must include both a cause and an effect. Here are some instances from the examples. (6.1) The heart causes the arterial pulse. (6.2) Cold causes the O-ring to loose its resilience. (6.3) Crossing a dominant plant with a recessive (cause) results in a dominant offspring (effect), regardless of if the pollen or egg came from the dominant plant. (6.4) Adsorption of phage to bacteria causes transfer of phage DNA to the interior of the bacteria. (6.5) Applying an electric force, opposed to the force of gravity, to charged oil drops causes them to hover, if it balances the gravitational force. (6.6) A post injection with sufficiently low momentum (cause) enriches the overlean wake of the main injection enough to render it combustible (effect). (6.7) A longer tail ornament in the male widowbird causes greater mating success.
6.3 In examples 6.1–6.2, no precautions are needed because the effects clearly arise from the treatments. (6.3) Mendel's large samples made it easier for him to see the patterns (there is an element of randomness in how pollen and egg combine). He also crossed female and male plants both ways to make sure that each sex contributed equally. (6.4) No controls necessary, but the sequence of experiments shows a gradual exclusion of error sources, such as adsorption to whole bacteria instead of fragmented ones, investigating the phage progeny before reaching a conclusion, and so on. (6.5) Millikan excludes error sources with each new version of the experiment. He decided to study the evaporation, he switched to individual drops, and he switched from water to oil. (6.6) Reference data were acquired during a load sweep using a single injection. This ensured that the post injection did not decrease UHC by increasing the load. (6.7) Control groups were used. Andersson also studied the birds’ behavior before and after treatment, and so on.
6.4 (6.1) Two hypotheses: “the blood circulates” and “its motion originates from the heart”. They arose from thought experiments and observation (see the quote about the butcher). (6.2) Hypothesis: “cold causes lack of resilience in the O-rings”. He arrived at it by bringing together information from a launch photo and discussions with engineers. (6.3) Apparently not an hypothesis-driven study. Question: “how are characters inherited in a hybrid cross?” Still, an hypothesis is tested by the test cross; “a double hybrid cross (AaBb × AaBb) produces all combinations because a double hybrid produces pollen and egg cells of all possible types”. (6.4) Two parallel hypotheses: “the genetic material consists of proteins/DNA”. It is not clear how they occurred but this was probably a current theme in the community at the time. (6.5) Hypothesis: “the electron has a definite charge”. There was a race towards finding this out at the time. (6.6) Two hypotheses: “the entrainment wave is a substantial source of UHC” and “overlean mixtures can be enriched by a post injection of sufficiently low momentum”. The first occurred directly from previous work by Musculus, the second occurred during discussion of the first. (6.7) Hypothesis: “female choice selects for extreme tail length in the male widowbird”.
6.5 Left to the reader. Now that we have identified the research questions, it should be obvious how distinctly the experiments address them.
6.6 To obtain explanatory knowledge the hypothesis must be explanatory: it must involve a mechanism. (6.1) Circulation of blood is a descriptive hypothesis, pumping by the heart is explanatory. (6.2) The hypothesis is descriptive. The greater hypothesis (that lack in resiliency caused the accident by leakage at the rocket joint) is explanatory but more evidence is needed to support it. (6.3) Mostly descriptive knowledge but the test cross tests an explanatory hypothesis. (6.4) Descriptive hypotheses. (6.5) Descriptive hypothesis. (6.6) The first hypothesis is descriptive, the second is explanatory as it uses the momentum of the post injection to explain the results. (6.7) Explanatory hypothesis that tests the mechanism of sexual selection by female choice.
6.7 Left to the reader.
6.8 Left to the reader.
References
1. Harvey, W. (1993) On the Motion of the Heart and Blood in Animals, Prometheus Books, Amherst (NY).
2. Feynman, R.P. (1988) What Do You Care What Other People Think? W.W. Norton, New York.
3. Mawer, S. (2006) Gregor Mendel: Planting the Seeds of Genetics, Abrams, New York.
4. Mendel, G. (1866) Versuche über Pflanzenhybriden. Verhandlungen des Naturforschenden Vereines in Brünn, 4, 3–47.
5. Hershey, A.D. and Chase, M. (1952) Independent Functions of Viral Protein and Nucleic Acid in Growth of Bacteriophage. Journal of General Physiology, 36(1), 39–56.
6. Avery, O.T., MacLeod, C.M., and McCarty, M. (1944) Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types: Induction of Transformation by a Desoxyribonucleic Acid Fraction Isolated From Pneumococcus Type III. Journal of Experimental Medicine, 79(2), 137–158.
7. Millikan, R.A. (1921) The Electron: Its Isolation and Measurement and the Determination of Some of its Properties, The University of Chicago Press, Chicago (IL).
8. Crease, R.P. (2004) The Prism and the Pendulum, Random House, New York.
9. Feynman, R.P. (1992) Surely You're Joking Mr. Feynman, Vintage, London.
10. Musculus, M.P.B. (2009) Entrainment Waves in Decelerating Transient Turbulent Jets. Journal of Fluid Mechanics, 638, 117–140.
11. Chartier, C., Bobba, M., Musculus, M.P.B., et al. (2011) Effects of Post-Injection Strategies on Near-Injector Over-Lean Mixtures and Unburned Hydrocarbon Emissions in a Heavy-Duty Optical Diesel Engine. SAE International Journal of Engines, 4(1), 1978–1992.
12. Andersson, M. (1994) Sexual Selection, Princeton University Press, Princeton.
13. Andersson, M. (1982) Female Choice Selects for Extreme Tail Length in a Widowbird. Nature, 299, 818–820.
