Mechanical clocks, the printing press, and the Reformation

Two of the most important technological innovations of the medieval period were the mechanical clock, and the printing press. The mechanical clock enabled greater coordination of people, while the printing press facilitated a rapid increase in basic literacy. However, I hadn't realised how closely linked the two innovations were, until I read this new article by Lars Boerner (Martin Luther University), Jared Rubin (Chapman University), and Battista Severgnini (Copenhagen Business School), published in the journal European Economic Review (ungated earlier version here). Boerner et al. link both technologies to the Reformation. As they explain, mechanical clocks are related to the printing press:

We argue that clocks contributed to economic and political change via two pathways, one direct and one indirect. The direct pathway was through technological agglomeration. Clocks required an immense amount of mechanical knowledge to build and operate, and their production required precision, technical skills, and dexterity in using different metals. These were precisely the type of skills that were useful for operating and repairing printing presses. It is therefore possible that spillovers from the clock’s presence encouraged adoption of the press.

And through to the Reformation:

It has long been conjectured that the press helped facilitate the spread of the Protestant Reformation, arguably the most important social, religious, and political movement in early modern Europe.

This link from the printing press to the Reformation has been established in past research, although its importance is still somewhat contested. Boerner et al. use data on 764 cities in Western Europe, with their key variables being: (1) whether the city had a mechanical clock by C.E. 1450; (2) whether the city had a printing press by C.E. 1500; and (3) whether the city was Protestant in C.E. 1530, 1560, and 1600.

Now of course there are a lot of problems with endogeneity and omitted variables in this sort of analysis. Boerner et al. deal with these problems using instrumental variables:

We address potential endogeneity and omitted variable biases by instrumenting for the presence of a clock with the town’s past experience with solar eclipses. The idea behind this instrument, which is also used by Boerner and Severgnini (2019), is based on the fact that eclipse activities stimulated the construction of astronomical tools such as astrolabes, which were the prototype of mechanical clocks. We instrument for the spread of the printing press with the town’s distance to Mainz, the birthplace of Gutenberg’s press.

Essentially, they run a three-stage regression model, where the first stage instruments for the presence of a mechanical clock using "the number of times a town experienced multiple solar eclipses over a one hundred year span between 800 to 1283". The second stage uses the instrumented variable, and instruments for the presence of a printing press using the distance from each city to Mainz (where the printing press was invented). The third stage uses the instruments to extract a causal estimate of the presence of a mechanical clock, and the presence of a printing press, on whether each city was Protestant or not.

You may be wondering about those instruments though, especially eclipses. Boerner et al. explain that:

The rationale for using eclipses as an instrument for mechanical clocks follows from two relationships: (i) the relationship between solar eclipses and astronomic instruments (astrolabes), and (ii) the relationship between astrolabes and clocks. Regarding the first connection, the observation and documentation of the course of the celestial bodies and in particular solar eclipses elicited a special fascination... Thus, the appearance of solar eclipses created curiosity to understand and predict these movements... This broad interest created a demand for the development and use of astronomic instruments to measure and predict the movement of heavenly bodies... In particular, astrolabes and in some cases astronomic water clocks were built...

The second link is that the construction of clocks was often motivated by astronomic instruments... and that the timekeeping function was stressed in European astrolabes... The fact that most early mechanical clocks were also astronomic clocks (and instruments) supports this argument further.

Then in terms of the distance to Mainz as an instrument for the printing press:

Distance to Mainz is highly correlated with the early spread of printing because the first printers were either apprentices or business associates of Gutenberg in Mainz. The secrets of the new technology – most importantly, the process used to cast movable metal type, which required a specific combination of alloys – was closely guarded among this small group for the first few decades of print... Printers also weighed cost when considering where to spread, and they therefore broadly spread out in concentric circles emanating from Mainz...

Ok, so running this three-stage analysis, Boerner et al. find that:

...towns that were early adopters of clocks also tended to be early adopters of printing, even after controlling for unobservable covariates via instrumental variables. This finding suggests that people with the elite human capital necessary to operate and repair clocks tended to agglomerate in the same cities, thus permitting spillovers when new technologies such as the printing press were introduced. Second, the printing press was positively and significantly associated with the spread of the Reformation... Third, while we cannot say definitively that the clock was statistically related or unrelated to the spread of the Reformation, a mediation analysis reveals a positive and significant indirect effect of the mechanical clock on the Reformation, indicating an important role for technological agglomeration in the spread of the Reformation.

Specifically, cities with a mechanical clock by 1450 were about 34 percentage points more likely to have a printing press by 1500, and cities with a printing press by 1500 were 33 percentage points more likely to be Protestant by 1530, and 36 percentage points more likely to be Protestant by 1600. There was some weak evidence that cities with mechanical clocks were more likely to be Protestant by 1600 (but not by 1530, so some more research on that point would be helpful in the future).

We can conclude that the mechanical clock and the printing press were two key technological innovations of the medieval period, and together they contributed significantly to one of the key social innovations of the period as well.