Francesco Redi and Controlled Experiments

Most people can name one 17th century Italian scientist based in Florence who challenged the widely accepted theories of Aristotle and was to influence the way Science was done in the centuries to come? There were actually two! The other besides Galileo was Francesco Redi. Francesco Redi is most famous for his excellent demonstration of the use of controlled experiments and his challenge to the theory of spontaneous generation.

When a scientist designs an experiment it is important to eliminate as many unknowns as possible. For instance, if one were trying to assess the health effects of a drug on humans, there are many factors which may affect health..simply counting how many of the patients get better or worse when given the drug is not good enough. We want to know how many got better or worse specifically from the drug. One solution might be to introduce a control to compare the drug-based tests against some standard case. In these drug-tests one group is commonly given the drug and another group, the control group, is given a placebo (commonly a sugar-pill with no known health effects). The subjects do not know which type of pill they have been given. The drug results from the test group can then be compared against those of the control group and we can get a better idea of which effects result from the drug. It is interesting that this important (and often ignored) advance in scientific methods was introduced only 25 years after the death of Galileo and only a few kilometres away from where he lived.

The Francesco Redi Experiment

Francesco Redi was able to disprove the theory that maggots could be spontaneously generated from meat using a controlled experiment. Spontaneous generation, the theory that life forms can be generated from inanimate objects, had been around since at least the time of Aristotle. Francesco took eight jars, placed meat in all the jars, but covered four of the jars with muslin. Maggots developed in the open jars but did not develop in the muslin-covered jars. Today controlled experiments are commonly demanded by scientific journals and are sometimes legally required by regulatory bodies (especially for pharmaceuticals). The image below is taken from Esperienze intorno alla generazione degl' Insetti (p. 187) where Francesco Redi published a description of the experiment in 1668 (see sidebar for digital copies of book).

Redi, Maggots and flies

Francesco Redi is often credited with developing the controlled experiment just as Galileo is often credited with introducing the modern experimental method. Both beliefs may be simplistic, however. Francesco Redi and Galileo Galileo demonstrated the effectiveness of their methods using very simple experiments, then explained their procedures and results in clear and compelling ways. These experiments were watershed events in the history of science. That is not to say that experimental scientists before Francesco Redi didn't realize the need to control variables or that the sequence of steps involved in Galileo's method hadn't been described by earlier natural philosophers (e.g. professors from the School of Padua). When Galileo was still a young boy, Giuseppe Moletti, the professor who he would eventually succeed at the University of Padua, decided to conduct some experiments on free fall by dropping weights in different media (see Timeline of Classical Mechanics). His test with free fall in water and air specified that the balls must be of the same substance, weight and figure in order to remove doubt. In the same book, when Moletti described dropping balls of wood and lead from a tower to demonstrate that free fall doesn't depend on weight (as Aristotle had said) he was careful to eliminate size as a nuisance variable by conducting the experiment with wooden balls of different sizes . Moletti's experiments certainly weren't as elegant as Francesco Redi's, but they indicate that he understood the need for controls [_1_] .

Being careful to control for the known variables doesn't guarantee that you will get the correct results. That is because "you don't know what you don't know". What if there are variables that need to be controlled that you don't even know exist. This could explain why the famous Tower of Pisa experiment actually came up with incorrect results. Many consider the legend of the Tower of Pisa experiment to be a myth. The experiment did occur. It was conducted by Vincenzio Renieri, a Catholic monk (see Galileo's Battle for the Heaven's) and not Galileo as is commonly thought. Vincenzio was a friend of Galileo's. Like Moletti before him, Renieri, controlled for size when he dropped two balls of the same size (one of wood and one of lead.) He came up with the wrong results. There was almost 2 metres difference between the heavier and lighter balls when they hit the ground. Galileo described similar results in some of his works. These scientists could not have known that they needed to control for human physiology as well. Modern experiments with humans dropping balls of markedly different weights show that there is a tendency to grip the heavier ball more tightly and release it more slowly [_2_] .

Francesco Redi and the Galileo Affair

Francesco Redi is very important to any discussion of events relating to the Galileo and the Church. These events are most often portrayed as dramatic evidence for the "the recurring clash between religion and science" (see Galileo's Battle for the Heaven's). But so many of the facts relating to Francesco Redi seem to conflict with this interpretation. Francesco Redi lived a comfortable life in Florence, walking the same streets and working for the same people that Galileo did (the Medicis). He died without encountering any problems with the Church. Depending on the author, Galileo's use of Italian instead of Latin was supposed to be a problem with the Church. But with Francesco Redi, it wasn't. Any challenge to Aristotle was also supposed to be a problem for the Church. But it was Aristotle who proposed life-forms such as maggots spontaneously generated, and Redi proved that to be false (although he continued to believe other life-forms might spontaneously generate). The Galileo Affair was supposed to have caused the decline of science in Italy, yet we we have one of the most important advances in the scientific method happening a short time later in the very same city.

The life and work of Francesco Redi provides cause to rethink the most common interpretation of the Galileo Soundbite; that it was, in essence, a conflict between science and the church. If the Galileo Affair demonstrated the inherent conflict between the church and science why wasn't this conflict repeated 25 years later when very similar circumstances arose. Could there have been other factors involved in what happened. Could Galileo's personality and his personal and professional disagreements with the other scientists of the day have played a more central role. Certainly, some of the most important historians and philosophers think so. And leaving personality aside, it could also be that Francesco Redi may have demonstrated better methodology in disproving Aristotle than did Galileo.

Copyright Joseph Sant (2014).
Cite this page (APA).

1. Laird,W.R., University of Toronto Press, The Unfinished Mechanics of Giuseppe Moletti,1576, , 147
Scientific books in the time of Moletti and Galileo were often written as dialogues where one scientist was explaining things to another. In this book the protagonist describes an experiment where two balls of exactly the same weight, substance and shape are dropped through 100 paces of water and 100 paces of air. When the passive participant in the dialogue asks why they must be the same weight, substance and shape, the protagonist explains 'To remove causes of doubt'. Shortly after Moletti describes an experiment where two balls, one of twenty pounds of lead, and the other one pound are dropped from a tall tower, and that they both reach the ground at the same time. He then mentioned that he controlled for size by conducting the experiment with balls of wood of different sizes. Moletti's book is dated at 1576.

2. Rutherford Aris, Howard Ted Davis, Roger H. Stuewer, U of Minnesota Press, Springs of scientific creativity, , 12-14
Thomas Settle describes an experiment by Dr. Donald Miklich who arranged for 51 students to perform repeated drops of balls with different weights then assessed the results. In 88 percent of the trials the lighter ball preceded the heavier one. This experiment used very specific experimental conditions and since the experimental conditions of the early free fall experiments were not always well described, the experiment might not properly relate to all experiments of the time.