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tokens: of the cores, and as such, our results are limited by our model. We note that spdust does not incorporate some important effects, such as internal thermal fluctuations, impulsive excitation due to high-impact ion collisions, and irregular dust grain shapes, all of which produce an increase in the emissivity of the spinning dust emission. Nevertheless, spdust is the only publicly available spinning dust model, and it has been shown to accurately fit observations of spinning dust emission (e.g. Tibbs et al. 2012 ; Planck Collaboration XV 2014 ; Génova-Santos et al. 2015 ). In addition to the limitations of spdust , we are also dependent on the parametrization of our adopted size distribution. For example, we assume that the size distribution varies only with b C , and that the other parameters, such as a 0, i and σ are fixed. Although Weingartner Draine ( 2001 ) were able to fit extinction curves for a range of R V values with these parameters fixed to the values used in this analysis, it is possible that these parameters will vary. For instance, if grain growth is occurring, then this will likely lead to an increase in a 0, i , which would have an impact on the amplitude of the spinning dust emission. However, in this analysis we follow the example of Weingartner Draine ( 2001 ) in assuming that these parameters are fixed, which enables us to compare our constrained value of b C with the value obtained by Li Draine ( 2001 ) for the diffuse ISM. Additionally, varying the electric dipole moment of the grains will also affect the result. Increasing or decreasing this parameter will result in a corresponding increase or decrease in the spinning dust emission. However, as discussed in Section 3.2 , our adopted dipole moment is rather conservative, and any such increase in this value would result in an increase in the predicted spinning dust curves, which would produce a corresponding decrease in the constrained b C values, therefore not affecting the results of the analysis. Throughout this analysis, we assume that all of the cm emission ( S 1 cm observed ) is due to spinning dust emission. However, as mentioned in Section 3 , it is possible that there may be a contribution from magnetic dipole emission. If this is the case, then this will decrease the contribution of spinning dust emission to the total cm emission, thereby further enhancing the observed deficit of very small grains. Therefore, ignoring magnetic dipole emission throughout this analysis is a conservative approach, and does not impact our results. Finally, we stress that this analysis is the first attempt to use spinning dust emission to characterize the properties of interstellar dust grains, and even with these limitations, this work demonstrates the possibilities of this new method, and as such we hope that it will be included in future studies of interstellar dust. 5 CONCLUSIONS By combining 1 cm CARMA measurements, with far-IR Herschel observations, we have constrained the